Well, it’s not a hard requirement, you could probably go with Lutris alone since it supports a lot of sources, but for ease of use it’s more straightforward to use separate specialized launchers, just like you’d use Steam and Epic on Windows in addition to all the (useless) launchers you’re made to install when you get some games from either, e.g. Ubisoft Origin.

So it’s not about how hard or reliable it is really, just which apps one prefers to use, on Linux you can arguably get a more centralized experience than on Windows since Lutris alone covers Steam, Epic, GOG, and others as well as a million other emulation platforms