SCG
Sahacogen(Chonburi) Public Co
stock NYSE

There's a couple theories about declining SCV "premium", no one really knows for sure.
1) Most premiums decline or disappear entirely after discovery/wide publication. Lots of AUM in funds that tilt SCV, not much in SCG, arbitraged away the premium.
2) The effect did exist in the past, but mostly because of how difficult it was to implement. If you read about the kinds of SCV stocks that famous investors bought in the 50s through the 80s you sometimes scratch your head and wonder "how did this ever exist/be allowed to happen?" Companies that were going concerns with real assets and customers would trade for like half their book value. Everything wasn't financialized and it was hard to get information, and this accrued more to not widely followed areas of the market.
3) Private markets have grown - small businesses with good prospects can easily raise money from private equity while keeping most of the ownership to the founders, reducing the need to go public until you're matured and more fully valued.
4) We used to do anti-trust - it's been obvious to people for a long time that if you let capitalism run the natural result is super firms dominating the market via anti competitive practices. There was a point in time when the government actively intervened to stop this, creating unexpected opportunities for smaller firms that probably would have died without this intervention.
5) Accounting for trading costs - some (not all) of the research fails to properly account for how difficult and costly it was 75 years ago to find information on a small cap stock, pay the costs to buy & sell it (spreads and commissions).
6) Economic growth, or lack thereof - there's a conceptual framework that suggests that small cap and value are "risk premiums" aka compensation for bearing the risk of economic growth. If economic growth is better than expected, firms in this bucket are more likely to exceed low expectations. On the flip side, if the economic growth is broadly weaker than expected or otherwise concentrated to a few big winners, the risk part shows up without the premium.
I honestly think no one in the world can tell you the "truth" of the matter. After many years of a mega cap growth led market I couldn't blame anyone for wanting to tilt away from that, although I'd warn you that very smart people were suggesting the same thing in 2013. Also, there's no way that the premium that investors got in 1950 could be the same today when you can buy any number of well put together quantitative SCV funds for almost zero cost.

There's a couple theories about declining SCV "premium", no one really knows for sure.
1) Most premiums decline or disappear entirely after discovery/wide publication. Lots of AUM in funds that tilt SCV, not much in SCG, arbitraged away the premium.
2) The effect did exist in the past, but mostly because of how difficult it was to implement. If you read about the kinds of SCV stocks that famous investors bought in the 50s through the 80s you sometimes scratch your head and wonder "how did this ever exist/be allowed to happen?" Companies that were going concerns with real assets and customers would trade for like half their book value. Everything wasn't financialized and it was hard to get information, and this accrued more to not widely followed areas of the market.
3) Private markets have grown - small businesses with good prospects can easily raise money from private equity while keeping most of the ownership to the founders, reducing the need to go public until you're matured and more fully valued.
4) We used to do anti-trust - it's been obvious to people for a long time that if you let capitalism run the natural result is super firms dominating the market via anti competitive practices. There was a point in time when the government actively intervened to stop this, creating unexpected opportunities for smaller firms that probably would have died without this intervention.
5) Accounting for trading costs - some (not all) of the research fails to properly account for how difficult and costly it was 75 years ago to find information on a small cap stock, pay the costs to buy & sell it (spreads and commissions).
6) Economic growth, or lack thereof - there's a conceptual framework that suggests that small cap and value are "risk premiums" aka compensation for bearing the risk of economic growth. If economic growth is better than expected, firms in this bucket are more likely to exceed low expectations. On the flip side, if the economic growth is broadly weaker than expected or otherwise concentrated to a few big winners, the risk part shows up without the premium.
I honestly think no one in the world can tell you the "truth" of the matter. After many years of a mega cap growth led market I couldn't blame anyone for wanting to tilt away from that, although I'd warn you that very smart people were suggesting the same thing in 2013. Also, there's no way that the premium that investors got in 1950 could be the same today when you can buy any number of well put together quantitative SCV funds for almost zero cost.