Sigh. Remember when Google Finance was great with easily the best charting software and easy lookup of key stats for a company? Then they decided a couple years ago to destroy it for no reason. I wish I knew why they made this horrible decision.
I really wish there was incentive to have products be "done". It seems that so many products get to a great state and then get made worse over time because we need continuous growth (Evernote immediately comes to mind. Others seem to feel similar about 1Password) or in the case of Google, get shut down.
I think the first charting software was written by one talented javascript guy. I think he moved on and the next person did not want to touch the code. Which is the story of many Google services.
Yes, it really was quite perplexing. I imagine the "reason" was to make it more mobile-friendly or mobile-first or perhaps just to standardize their properties more. However, as you noted, it really degraded the product. I went from a daily user to an almost never user.
"mobile-friendly or mobile-first" seems to be a trend in quite a few companies, in the last few years. The main problem is, the completely ignore the desktop design, viewing it as an either-or proposition, for some, unknowable reason. While it's understandable that much traffic is mobile, during office hours, especially during work from home (which will probably - at least partially - be a continued trend moving forward), quite a bit of traffic will be from a desktop/laptop. Simply ignoring this market share seems to be a fools errand.