Actually there are more then 1750 physical tier backers. So that's slightly above 10% of all backers that are getting a not so physical copy of the game.
I really hope they are going to change this, or at least let us get a proper game disc after the game has had it's initial patching done.
I wasn't counting the higher tiers, whether that was fair or not I don't know, but I would expect many collectors not to open the box and those higher tiers do explicitly say they include a digital copy as opposed to the two lower tiers that say they don't. I don't think that 1750 or 300 really matters when it comes to the reasoning as to why it's just a steam installer though, either way they'd have to have separate installers etc for patches for people who have (1) already paid and (2) are likely to be considerably less than 1% of total sales; plus complaints about not having physical copies of expansions and the like. I'd suspect that process was a pain in the arse last time and they want to avoid it this time.
*well, theoretically and per description. The physical tier descriptions are a bit of a mess, if not outright misleading, I agree. A steam installer with (presumably) a code is a digital copy of the game rather than a physical one, by any sensible measure.
Sure the higher tiers also gets a digital copy, but they are still physical tier, and sure most higher tier backers might not open their box but that doesn't mean that what they are getting in the box is unimportant. Then you might just as well just send them an empty box, why even bother putting anything in it if they aren't going to open it?
The thing is that they could just put the PoE2 steam or gog installation files on the disc. Meaning that there never will be a need for different patchers and installers, everything is going through steam or gog.