Mostly because it leads to them costing more, which granted might decrease over time. But I've seen a few developers who released physical versions all say that they make more money from digital because of all the other guys who take a cut with the physical. Personally, I prefer money going to the developers than to some faceless publisher who just does the menial task of creating the physical item.
I see your point, but it's not like selling digital gives you 100% net profit. There is a cut taken out of that too. Additionally we don't know what the contract agreement between the devs for Teslagrad and it's publisher are. Often times the publishers take up quite a burden and are tasked with advertising, marketing, manufacturing, distribution etc.