Buying altcoins is not diversification. When bitcoin goes up, altcoins go up. When bitcoin goes down, altcoins go down much more. You are not negating risk at all by buying altcoins, which is the whole point of diversification. If you get really lucky and catch some random pump and dump you might make a little profit, but the vast majority of people who hold altcoins lose money. Just ask anyone who bought pretty much any altcoin during the bullrun at the end of 2017. 99% losses from their ATH is commonplace.
If you want to diversify your investments, look at vehicles outside of crypto altogether.
I know that all altcoins depend on bitcoin prices but it requires just a little jump in the price to see altcoins as profitable while those investing in bitcoins need to have a good investment of 1000+ USD to get a good profit which is not in the case of altcoins where you can invest as little as $100 and see yourself earning a good profit. Not to mention the amount you pay as fee in bitcoin transactions and confirmation time.
There are many other investments one can make but here I have found altcoins more profitable than bitcoins as these altcoins start from a price of $0.01 or less where bitcoin was in the start.
If a project has stopped being developed or worked on because the price has fallen, that's a pretty sure-fire guarantee that it's a trash project and the creators/developers are only in it for the money.
That's true but since the market is now almost dead, can't say the project was trash or not as some projects were really doing great when they were launched.