Unless on DVD is an obscure and widely unknown yet superb material, I don't see why would you still do that.
Back in the day I had to import DVDs as a movie or series I wanted to watch were not available where I live. Streaming? What streaming? Dialup was still a thing.
The problematic part with imported DVDs (and VCDs) was in some cases there were no subtitles included, only a transcript, so I had to rely on fanmade ones. Another problem was different cuts. In some cases you, I mean me, had to be careful which version I'm gonna get because different distributors felt a need to cut half of the movie away, okay not half but too many of minutes (after Snowpiercer "scandal" it seems movies mutilation depending on region won't happen any more).
We mentioned Nic Cage in TW series thread, someone mentioned bees scene ofc. Did you know there are two movie versions where the bees scene is cut out from one? Well, if you didn't, now you do.
Today, streaming services are trying to cover as many titles as possible, not because they love underappreciated and underrated stuff but because if they won't compete with other services they'll lose subscribers. Why would someone pay for a service that streams only mainstream garbage you've already watched or are avoiding like a plague? Some titles are still not available on streams of course, for example totally crazy
The Bride with White Hair. Oh you've never heard of it? I'm shocked.
I'm trying to say, something is not streaming anywhere and you're desperate to watch it? Okay, go for optical media. But buying Transformers movies collection on DVD? Man… How about investing into phonegames instead.
EDIT:
Forgot. Streaming sometimes brings a better quality. An example is the only movie I could bare Jim Carrey in. Can't stand the guy elsewhere.
Pink Cadillac DVD is not in the best shape (yea, I have it), it's blurry, yet the streaming version is crisper. No, actual bluray doesn't exist for this one, seems a version for streaming purposes got "polished" or the one for DVD was screwed but whoever distributed it didn't care.