There is a bias in software: if you can see it visually it’s worth less.
That bias has generally resulted in lower compensation for front end work irrespective of inherent technical challenges. The result of that bias impacts hiring and trust which then dictate approach and implementation.
I think this could be reformulated: the result of backend development has less immediately visible consequences, thus more potential for catastrophic errors hence requires more testing and planning in advance (whereas UI testing in the limit is difficult).
Also, if anything, the last couple of years have shown that front end development, and web dev in particular, is highly prone to churn. Hence managers might be tempted to think of a front end as a throw-away component that needs to be redone anyway a couple years down the road when no web dev wants to touch legacy code not using the latest and greatest tech stack, and the relative difficulty of UI testing adds to that. Now why there's so much churn in web dev is another question. One hypothesis is that it's a field seeing lots of freshman; as such, the wealth of frameworks we're seeing is left as a trail of those younger devs learning to make sense of webdev ;) But maybe it's simply that requirements and expectations are changing all the time.
Personally, I'm not at all of the opinion that frontend coding is or should be less valuable than backend.
It's the other way around. What you can't see is harder to sell.
However, because people like to see things, there are more people wanting to do frontend and hence the compensation is lower.
The same with game developing. This is definitely not easier than frontend or backend, probably harder. But still paid less, because it's so popular and many people want to do it.
In web development the average wage for frontend work was lower because the skill level required was lower. You don't need a lot of knowledge to be effective at building websites with HTML/CSS/Photoshop and a sprinkling of javascript/PHP.
During the same time wages for people building frontends which needed more engineering knowledge (early mobiles, WinForms, those horrible old Java frontends) were higher because there were less people capable of doing the world.
In 2021 web development has moved on to the point that we're often building websites in fully features programming languages with heavyweight frameworks (React/Angular). They are paid well. You still see people who work with HTML/CSS/Photoshop and they are generally paid less.
See: Quality Assurance and the different between people who can test manually and who can automate their work.
That bias has generally resulted in lower compensation for front end work irrespective of inherent technical challenges. The result of that bias impacts hiring and trust which then dictate approach and implementation.