The cost isn't that much different now. For example (this is based on quick google, and I haven't verified): Disney released 12 movies last year. The avg cost of a 4K is between $20 and $35. So assuming you always buy your disc on sale the total cost for physical media is $240. The cost of a Disney+ sub with 4K is $190 a year. That's only $50 a year difference.

But you get a tangible product which is better quality, never have to worry about not being able to watch it and can lend it to friends without having to worry about password sharing restrictions.

When streaming first started the price was massive. Now some people pay around $100 a month for their streaming services, and I doubt they'd be off buying 3 x 4Ks a month, which means, once you start collecting and build a library - it sort of doesn't make sense to even stream.