I feel like this depends on the type of dev. If you write C code for microcontrollers then who cares, but if you do web dev then using a generic template not authored by you seems like a bad sign, no?
But part of why I consider it arbitrary is it's easy to come up with contradictory criteria, each of which might make sense. (-1 for using latest technology on a personal website, since it shows they buy into hype/resume-driven-development. -1 for not using the latest technology, since it shows they don't know the tools of the trade). I think this bleeds from trying to judge someone's professional capabilities as part of a team, from something produced in their spare time.
Portfolio sites are used to showcase the developer's work. If the developer's work sucks then it doesn't matter if it was done just for fun or as an extension of his CV.
Hell, I can’t even find time to pick a template and design the look and feel or choose what content to put on my own website.
You get zero signal from the fact that someone decided to use a default template.
If I want just someone to write simple stuff I have whole of India to choose from and they are way cheaper than you. If I'm looking for a web dev from western market I'm looking for highly talented people and if you can not showcase that talent then what good are you for?
From my experience thous who have no personal projects of passion that involve programming to any extend usually aren't that good at their job. That obviously doesn't mean that you can not or shouldn't have other hobbies that are not computer related, but again if it comes down to two candidates and one has proof of work in their github profile then the choice isn't that hard to make.
A personal website is not a software development project. It is not something to use to evaluate a developers technical skills. When you have a real project on the line, then you will see the real skills come out.
For a personal website, I’d expect a developer to give a fuck enough to develop something on his own.
Especially since "I'd expect a dev to not rewrite everything themselves, and leverage what's already available" is just as reasonable.
There's not exactly a specific "right answer" about whether you need a personal website, what it should look like, or how it should be written.