Are you asserting that developing an understanding for a vanilla web codebase is somehow worse than figuring out how to upgrade an Angular2 project to Angular8?
The biggest reason we use "custom" framework is because all the "standard" frameworks change too rapidly to support our business model. They also fall out of support before our B2B contracts expire, creating very difficult situations at due diligence time. We sell software to banks, so we don't get much room to work with regarding our 3rd parties.