They do it because they are looking "to get rich" and think one of these alts will have a huge run. It's also physiological in that ypu can buy some of these alts for pennies or less than pennies so they can buy a lot of coins. It's all relative but there truly is a theory that alts are cheaper. Also greed. Greed drives the entire meme market
Also the fact that there has been history of some low cap alts suddenly turns into multi billion market cap coin is what motivated them the most.
so many people actually looking for that kind of hidden gem and since such coin are quite frequent in the bullish market, people invests more and the market of alts become much more active with good gains and the cycle will be endless.
but I think the idea that bitcoin market cap is already too high that the volatility is low might also be huge contributor to the fact that there are many people who seeks volatility to profit off and alt serve exactly just that.
it all comes down to get rich quick scheme at the end of the day.
Which is a very very rare thing and yet people still think that it is possible for the ones they pick to become like that. I mean we know that it happens once every few thousand projects, which is why its such a low chance for it to go up like that, and we avoid it and carefully calculate our investments, and yet these people do not know that, or maybe know it but willing to take the risk and they end up with a lot of mistakes, which there is no need to do any of that.
I feel like its clear for all of us that bitcoin is the one to go, but even if we pick altcoins then we pick strong good coins, whereas these people pick stuff that may do 100x or crash and burn. If the chances were 50-50% then I would say it worths it, but the chances are mostly 0.001% to 99.999% so that is why there is no reason for me to take this type of risk, it doesn't make sense and there are some situations that caused this to be a very different situation without a doubt.