I think the era of "poor software for fantastic hardware" is coming to an end.
UI development is an even more special case here. The customer buys the machine which runs the code, not the company. So sadly "good enough" is the standard.
One example for me here is the "switch product option" button on Amazon listings (e.g. switch green to blue color, smaller to larger model). On my phone this sometimes takes >5 seconds to properly load. Horribly optimised.
Just as an example, the cost of one week of engineering time corresponds to tens of thousands of vCPU-hours, which is many years of CPU time.
As such, it only ever makes business sense to optimize code either when it has bottlenecks that can’t be fixed by throwing hardware at it, or when it’s so inefficient that it can be sped up by several orders of magnitude.