Because nobody has recently managed to follow through with a real improvement.

Most of the people who have tried to update style have taken rather drastic approaches that were likely to have too much down-side and then never managed to get to the finish with a working replacement to try to get applied.

If more people came up with much smaller improvements and did the work to really vet them and make them quite explicit and then worked with pmdev members to get them applied, then we would likely have much more progress on presentation.

For my part, I just made one tiny change as documented in Tidings. The "Large Code Font" option is now enabled for anonymous visitors. I believe it is a better default experience when you look across a wide range of potential client environments. For some anonymous visitors in some environments, the size of the font in code sections will now appear noticeably larger than the size of the font of surrounding text. But that is less bothersome than the client environments where the code font ended up small enough that it was difficult to read.

New users still get "Large Code Font" disabled and so may want to visit Display Settings to change that.