Because before we had local desktop applications that were substantially less secure, with far greater default access rights (even root/admin in many cases).
Webapps that execute in a silo-ed virtual machine with only access to their own data (without express permissions), is a substantial security improvement (and also doesn't require the user to install anything).
To be honest the people who want to visit a website, for free, and then insist on how that website is delivered are super entitled. If you don't want to execute a site's code in a browser's secure context then don't, but you cannot whine about it like they owe you.