I'm willing to accept your argument that a Mac is not a general purpose computer. It then begs the question of why these devices are so popular for software development...?
https://insights.stackoverflow.com/survey/2021#technology-mo...
MacOS comes in at 25.19%. Even Linux is higher at 25.32%.
Meanwhile, Windows is 45.33% (over 48% if you include WSL, which was counted separately).
82,719 responses on the operating system question too...
(I'm not claiming that that's true - simply that your implication that "it is necessary to have a general purpose computer in order to develop software" is untrue)
I think a lot of this will happen under the goal of unifying the laptop and phone/tablet experience.