Backend code talks via APIs. Things need to be well-defined so that machines can communicate.
Frontend code has that but has to talk UI, too. That's a much looser-defined interface relying on human nature and perception to work. Meaningful performance is based on that perception and never in the areas that were well-designed. Frontend security is something you can't just hide behind your DMZ. And the design much more susceptible to changing fashions and the whims of PMs and execs. And those people and more think they know how to do your job because it's something they can see.
The same issues that make frontend harder to do to certain degrees of “right” also make it fuzzier – with backend, if its not done right it (perhaps intermittently) definitely, undeniably doesn’t work.
Frontend not done right is often fuzzier and debatable, so it is simultaneously harder to do frontend optimally and easier to do frontend well-enough to get away with.
This is, perhaps, why pure front-end work tends to pay less well. Quite a lot of the time, good enough to get away with is, well, good enough to get away with.
Frontend code has that but has to talk UI, too. That's a much looser-defined interface relying on human nature and perception to work. Meaningful performance is based on that perception and never in the areas that were well-designed. Frontend security is something you can't just hide behind your DMZ. And the design much more susceptible to changing fashions and the whims of PMs and execs. And those people and more think they know how to do your job because it's something they can see.
Yes, backend is easier.