New innovation is leading to new Altcoins and developers anticipating innovation faster is a big part of development strategy.

Weed out old and outdated coins

Many coins have been started when Cryptocurrencies were less developed and much less innovative.
And here it is a big problem for many Altcoins: using outdated Blockchain technology.

A good example for such an issue is Tron.
Tron was developed from Justin Sun to compete against Ethereum 1.0.
But Tron was such a badly coded coin, it couldn't even compete against Ethereum and lost many marketcap against Ethereum.
Now, since Ethereum 2.0 is launched, Tron is completely embarrassed because of its old tech.

Tron is based on an old technology where more innovative coins are outperforming Tron massively.
Tron is losing relevance very quickly compared to such new and more modern coins like Ethereum 2.0, Avalanche or Algorand.

One more old coin is EOS. It could not meet expectations and was even place 5 in market cap until it is now very irrelevant. People still holding EOS are having a big loss.
Lucky, who got out timely, to prevent a loss.

Conclusion

We should sell such outdated coins like Tron because such coins will become more and more obsolete over time.