yes lots of shitcoin / altcoin die because they have no further development, as developers / teams in their projects have left and don't care about their road maps anymore and in the end make altcoin dead / worthless at all. and you cannot fully assume that it is caused by the erc20 platform? That is not true. because the erc20 platform has so far developed well, the question is how developers develop their erc20 tokens, because the important role in the project is the developer of the project.
Those projects die not only because there are less demands from investors over time, or their developers abandoned those projects, but also due to the high competition in crypto. New projects born every day, and by now we even heard about blockchain 4.0. Old projects, if not grown, adapted will be hardly to survive over years.