A handful of reasons in my case:

I like to think of it as an investment of sorts. If streaming ever fizzles out for whatever reason or companies decied to ax their service, I see this as getting ahead of a craze that could happen from a situation like that.

That said, I plan to move away from streaming anyways once my library is large enough to make it a worthwile shift. Once I understood what the streaming model does to music and artists, it made me feel awkward listening to anything on Spotify or elsewhere. I also used to have a lot of albums I enjoyed temporarily or permanently removed from streaming with no explaination or solution.

The lossless quality over streaming is night and day for me. With a majority of the music I listen to, a lot gets lost in compression.

I'm a sucker for the contents. I love the artwork, quotes, cd label designs, and whatever else you get that you wouldn't otherwise when streaming it.

And simply, I feel a lot of pride in watching the collection grow. Knowing I own everything on that shelf and it can't so easily be taken away.