Do they? I'm not so sure.

While exclusives certainly limit access to those who own a certain platform, they also usually benefit from being developed for one specific piece of hardware in terms of polish, stability, etc. Some of the most ambitious and polished games ever made have been exclusives, mostly on Sony or Nintendo platforms.

They also help to engender a distinct identity for each platform, IMO. This is a more ephemeral thing, mind you, but I think that both Sony and Nintendo have succeeded in carving out a clear brand identity for themselves via the kinds of exclusives that they've gotten onto their platforms from their stables of first- and second-party developers. Does that make sense, or am I just talking out of my ass at this point?

More options is always better for consumers, of course, but I think that exclusives also come with their own set of unique positives as well. I'd be curious to know how most people feel about this topic. I could very well be an outlier here.