I'm curious what the technical reasons for you to choose to re-build it as an SPA rather than just gradually improve the layout and some new features? I don't u

I'm curious what the technical reasons for you to choose to re-build it as an SPA rather than just gradually improve the layout and some new features? I don't use Reddit as an application. I have my favorite subreddits in my bookmark bar in my browser, under a folder called "Reddit". Everytime I switch between them I am forced to do a re-render from the ground up now, which takes about 4-5 seconds on my quite beefy hardware and network (overclocked i7, TITAN X, 1Gbit fiber), while the old design only took a second, 600ms of which were TTFB for the main html of the page. I understand if your reason for a redesign is to keep new users, but what I don't understand is why it had to be a single-page application?