Just like what happened to HTML and CSS.
Like most other web-SaaS tools, they aren't browser based because its better for the user. They sacrifice speed, native functionality, and usability for owning via server-side control over your wallet on a subscription plan.
The startup market in no-longer customer driven. It is investor thesis driven.
I can concede that SaaS can be, in many cases, be merely investor driven, but I cannot concede that Figma is one of those. Even being investor driven, such as having a subscription business plan, is not bad for the customer per se, as a sustainable business is better than a dead one. Software costs money to make, and more importantly, to upkeep and add features too. I am not sure how you can expect one time fees, especially for enterprise software like Figma is (personal plans are free), in this day and age.
Can you imagine that if designers before this wanted to move an element in a list, they would have to move every single one instead of having some drag and drop swap functionality? That if they wanted to dynamically change a button size for the text inside it, like we can do easily on the web, they simply couldn't?
Basically, Figma is turning design more into something like front-end development, doing things in a design program that engineers could do normally with code. This is because the developers of Figma are themselves coders rather than designers, so they know what real ease of use should look like (ironically). This is the fundamental corporate culture shift that is the difference between Figma and others like Sketch.
Of course, you could go all the way and simply turn the design software into a web/mobile development framework, which is what software like Framer [1] does, which is literally a design software built on React, and it can spit out React code for you once you're done designing.
[0] https://www.figma.com/blog/announcing-auto-layout/
[1] https://www.framer.com/