I don't think the number of shitcoin projects are declining because there's around 21K coins right now on CoinMarketCap, few years before it's only 2K. Growing up from 2K to 21k for few years is really a huge number difference.
I think Shitcoins hype start since 2017 which is already 5 years right now and there's nothing changed so far.
Although I really hate shitcoins, but I don't see any sign shitcoins era will going to end.
Until everyone realize decentralization and privacy is a big concern, shitcoins era will end ASAP.
I think the same as you, I would love for shitcoins to disappear this very moment but this is not going to happen, people love to speculate and to try to earn a lot of money quickly and since coins like bitcoin or ethereum move too slowly for their tastes then they try to look for alternatives, and shitcoins are there to fulfill that need, after all we need to understand that shitcoins as much as we dislike them have a reason to be and if there was not demand for them then they will not exist, and since I believe such a demand will always exist then I can easily guess shitcoins will keep existing as well.