There are lots of technical reasons why web apps are slow, and this is a technical site so, as a community, the discourse tends to over-index on "react/electron/python/whatever is slow".
But these are the messy human + economic reasons why things are actually slow.
I'd add some nuance to (2), that even small corporate projects are often built by companies that are explicitly incentivized to build as quickly as possible, any other barometer of success goes out the window.
If you use software developed by companies or projects that are outside (1) and (2), you'll find it is actually pretty fast, subjectively.
But these are the messy human + economic reasons why things are actually slow.
I'd add some nuance to (2), that even small corporate projects are often built by companies that are explicitly incentivized to build as quickly as possible, any other barometer of success goes out the window.
If you use software developed by companies or projects that are outside (1) and (2), you'll find it is actually pretty fast, subjectively.