teceem: For some people... other people have slow internet access or download limits.
satoru: There's quite a few problems with that
1) Retail games for PC are kinda dying so even getting one is a minor miracle
2) Many retail games literally just ship a cd with the steam installer and the cd-key on a piece of toilet paper and that's it. Aka the disc contains literally nothing
3) Even if the disc contained some data, it has a usefulness of about 1 week at best. You will absolutely have to download a day 0 patch no matter what, as the disc data is already fairly old (going gold does not mean anymore that the dev team stands still so there will always be changes to download no matter what). After just a few post release patches, the data on the disc will be so old and out of date, steam will outright download the entire game again since 90% of the data on the disc is worthless and cannot be patched.
Sure, I know all that... but Steam activation for retail games has been around since 2010-2011 (or something like that). You're mostly referring to the more recent ones. It's perfectly possible to find new copies of retail games with steam activation that have been originally released more than 5 years ago.
Also, some retail games, even now, are GOTY or "Definite" edition with all data on the disc and no updating needed. But I know they're disappearing and often being replaced with code-in-a-box ones (again, for recentish releases).
I'm not talking about myself. I have a friend that cares more about having a physical box than about DRM. He has a cheap internet package (=low download limit) and still likes to buy some of those older physical Steam releases.
Me, I don't want DRM anymore. On rare occasions, I'll buy a Steam game if it's REALLY great and very unlikely to come to GOG (e.g. the Resident Evil ones). I'll only pay a ridiculously low price and I'll download a "DRM free backup" somewhere.
I love physical releases, but even before online activation those boxes had become sad containers with little printed (or other) contents in them.