Honestly, in my experience, the drive for bespoke styles isn't from developers, but from product folks and stakeholders. For instance, I once had to build a CMS

Honestly, in my experience, the drive for bespoke styles isn't from developers, but from product folks and stakeholders. For instance, I once had to build a CMS UI with a dropdown where users could pick how they wanted to sort their search results. The product folks also asked me to add a "Show Translations" option in the dropdown, which wasn't a sort order, and could be toggled separately. They insisted that it needed to be in this dropdown and not a separate UI control, and since they generally know what the users want better than I do, I went with it. I've semi-frequently had to build custom tree views and tree selectors with multiple modes of operation and various amenities. And sometimes the way those complicated widgets are built requires that we customize more basic components like split-buttons or dropdowns to match so that users aren't thrown off. Sometimes all of this can be accomplished by taking a library like Bootstrap and applying a theme. But sometimes the theme gets so intense that we realize we're basically just building Material UI on top of Bootstrap's code, and it makes more sense to use that library instead. And as mentioned before, sometimes there are just things that we can't get from Bootstrap or Material, but that we're going to use fairly often (last I checked, Bootstrap didn't have a 5-star rating widget). The "It's Fashion!" narrative seems very appealing to people on HN, to the point that I'd advise people to double check that they're not falling for confirmation bias before proffering it as an explanation.