Fundamentally, it is easy. Its not really difficult to learn to lift weights correctly. Literally, watching one video on how to do a bicep curl will teach you how to do a proper curl. Not difficult at all. Just takes a small bit of knowledge. I wouldn't equate this with something difficult really.
Yes, you need to know your anatomy if youre a competitive powerlifter who is lifting 800 pounds. Grandma doesnt need to know the intricacies of her anatomy to correctly perform a 5 pound dumbbell curl. There is a world of difference.
And after that you go to gym and do some barbell curls, some dumbbell curls, some hammer curls, some cable curls, some concentrated curls, some preacher curls, some decline dumbbell curls, some overhead cable curls, some incline dumbbell curls, some cable rope curls, some alternating curls, some drag curls, some prone incline curls, and some Zottman curls and if you would able to use the Vince Basile's Wonder Curl MachineŽ, you would use that also. You do at least 6 set of each, 15 to 8 reps per exercise and so on. And this is easy?
For most of the people it is too difficult to understand what and how much they should do, so if you have 12 dozens of different exercises per muscle group, how it is easy to choose what would be efficient and good just for you? It is usually done by trail and error, and that take years after years. Why it is done like that? Because no one would listen any advice, because everyone knows these things better than anyone else.
And what and how much is only little part of the knowledge, you should know also when, why and how, meaning that different order of curls leads to different outcome, and it is just same with all training. Then you have all the techniques and special techniques to choose from, do you use super sets, giant sets, rest pause, negatives, forced reps etc. etc. and you should know when to use them and how. In real life you get your knowledge a drop by drop, and even that is hard to swallow, so it is just stupid to say it is easy. You see, it make no difference if you are young men or old lady, you benefit more per the time unit if you do it right, and the older you get, the easier you get injuries if you don't know how to lift smartly