Think about it like, would you rather subscribe one service or subscribe Netflix, Hulu, Disney, Apple and others separately?
It's better to use one best wallet for each coin but it's a little clumsy. So, many people are looking for a wallet that offers them the most coins. Sadly, they rarely care about the safety, they only start caring about it when they experience hack or loss.
by using 3 wallets you can access about 90% of long term cryptocurrencies investing because most of them are tokens based on a specific blockchain such as Ethereum for example.
Otherwise, many tokens are not worth withdrawing from platforms or due to rapid technical changes and the possibility of freezing them, there is no benefit from keeping them for the long term and if you are an altcoin fan and looking for security, buying HW is enough.