The argument is that, for most people, letting them do what they want with something they don’t really understand is not a good idea. In this case it also creates a support headache for Apple. At first, they kind of tacitly accepted that jailbreaking was just going to happen and didn’t really actively fight it other than to close exploits used to root devices. As more and more people did it, for the reasons outlined above, more people wound up with bricked, or otherwise malfunctioning iPhones. When they went to Apple to fix it, at first there was an effort to help (you know, to retain customers), but they had voided their warranty. Because of that, Apple wasn’t really interested in spending lots of time troubleshooting something when they didn’t really know the full status of the OS (b/c there were multiple ways to jailbreak, and most of the fools taking their rooted phones to support didn’t understand enough to tell them what all was done beyond, “my kid’s friend said this would be cool”). Eventually Apple washed their hands of the whole thing and started refusing any support for rooted phones. That part, I have no problem with. They also started actively working to stop folks jailbreaking. That part, I thought, was too much. Just tell them they void the warranty by jailbreaking and refuse support. They dug their hole.

FWIW, I use an iPhone for personal use and android (Pixels) for work.