You are right, they will become worthless and its better not to hold them, who wants to hold such coins anyway? Shitcoins can bring huge profits too but holding them is wrong, I can name few shitcoins can gave me good profits that I can never earn from Matic, Luna and other popular altcoins.
You indeed do have a point, quite a lot of investors take altcoin investment to be short term, they buy and pull out when they make ROI, they go at it again with some other shitcoin and try their luck over again. But the thing is this, even if they (altcoins) are short term projects, there are no guarantees that you would make profit with them even in the short term, why? Majority of them are pump and dump coins as we all know, so there is actually a very high chance of you buying at the wrong time (so close to the dump), and even if you are not holding them you would still incure losses in the short term. And the thing with most of this losses is that it is somewhat '
permanent', what i mean by that is, when it dumps, more often than not that is the end of it all.
Thus in the light of the above, mind you that the altcoins you highlighted above as 'popular altcoins' are really no different from shitcoins, they are more or less the same. Many investors go ahead to buy many altcoins all in the name of diversification, hoping that one or two produces returns, sometimes it works out, sometimes it don't, what they do not understand is that in the long run, they are actually spending more and gaining less, they prolly think they are getting the coins for cheap and it would save them a lot than buying Bitcoins, but that is not true. If they draw up a strategy, DCA for example, they would be able to grow a decent Bitcoin portfolio in the long run with all of that money, which would definitely be profitable for them somewhere along the line.
Having said that, i am not saying you should forsake the shitcoins that you claim have given you great profits, neither am i saying you should just jump into the Bitcoin network, all i have said above is for the sake of other newbies to really understand why buying Bitcoin for the long term is a much better investment, but of course they must have to do their own research. (You as well).