I pointed this out in 2013 only to be literally shouted down by my manager. I did so again in 2017 under a different manager on the same team with the suggestion that we investigate using SPAs and RESTful frameworks only to be told that Razor Pages was the way forward which, while an improvement, didn't do any wonders for our ability to attract/build technical talent or create rich user experiences.
As a sibling comment points out (in a sentiment that I've echoed on HN before):
> ASP.NET Web Forms are a complete trainwreck and an abuse of HTTP and other basic web development standards (e.g. by using javascript: URLs and POSTing forms for every single interaction with the page). It is broken by design.
You can probably see why developers that chose this framework in the first place aren't interested in upgrading... learning actual web standards and state management isn't something they wanted to do in the first place.