When did retail investors truly start becoming "bag holders"?

Actually, it didn't happen suddenly in a certain year, but rather the pricing power gradually shifted from the public market to the fundraising stage.
The earliest ones, like the E group, ICO price was $0.31, and the secondary market was just over $0.4; the primary and secondary prices were almost the same, so even if you missed the earliest round, your costs weren't too far apart, and the upside was fully reserved for the market later on. Between 2018 and 2020, for example, SOL, there was a clear cost stratification: seed round at $0.04, secondary as low as $0.5, a tenfold difference, but the issue was that at that time, the narrative and growth hadn't been exhausted, and the market was willing to continue overestimating valuations, so retail investors, although paying a bit more to enter, still managed to catch the main rally afterward.
The real change happened after 2020, not because projects got worse, but because the gameplay changed. The number of funding rounds increased, valuations were continually front-loaded, and prices were "designed" before listing. For projects like OP and STRK, it was no longer about discovering the price through going public, but about cashing out at pre-set prices in the market. During the private fundraising stage, FDV was continuously inflated, and at the moment of listing, secondary market prices weren't about room for growth but reflected already overdrawn valuations. The price fluctuations you see are just volatility; the real profits had already been distributed in the unseen stages.
As a result, the structure changed completely: previously, primary was cheap and secondary was used to grow the cake together; now, primary sets the price, and secondary is responsible for providing liquidity. Going further, low circulating supply combined with high FDV became the norm, making it easier to push prices higher and exit. Airdrops became a stabilizing mechanism, and TGE increasingly resembled a liquidity release point rather than an origin.
So, the issue isn't that retail investors have weakened, but that the upside potential no longer remains in the public market. If you still play with the old logic of "holding and waiting for the bull market," you're likely to burn yourself at high valuations. Those who can still make money now are essentially doing something different: watching the rhythm, monitoring unlocks, seeking liquidity windows, thinking about exiting before entering. In other words, this market has shifted from a game of eyeing the best opportunities to a game of who understands this allocation game better.