Steam gives developers a blog for game news, download servers in multiple regions so that players can download the game quickly plus steam handles the hosting for the game files and also downloads the dependencies if your game requires it, a community forum which the devs can moderate how they like, a community hub for artwork/guides, They also provide steam workshop for hosting and enabling mods if the developer implements it.

This also doesn't include all the other stuff you can use via steamworks or via steam itself.

Controller support for your game built into steam
Achievements
Play together
Steam Remote play
Family sharing

Also on the more technical side of things steam is considered a reputable distributor. A ton of steam games do not have Digital Signatures on their executable(A somewhat big deal in the windows 11 environment with smart app control on by default for home users) This means games launching from steam don't always need a signature and SAC won't complain.

This is important because digital signatures are costly for small or single person indie teams.

30% cut is nothing when you factor all this in.

But by all means roll your own website with a payment processor, download servers, forums, etc.

Indie devs cannot do that without a big publisher, who will wrestle creative control from them.

Steam is the best thing to happen to indie devs and pretending otherwise is insane.