Usually what determines the difficulty is how a particular brand and model of rim likes or dislikes the tire, but there are some tires like ones that are more puncture resistant will tend to be more difficult to put on because the sidewalls and the tread are stiffer due to heavy duty puncture resistant liners.
I happen to prefer my tires to be difficult to put on because if by some slim chance I have a blow out, which is rare, but could happen, the tire will stay on the rim instead of peeling off fast and then your skating on your rim as well as destroying it.
I think most people who claim to have a difficult to install tire is simply due to not knowing how to put a tire on properly, so instead me beating my head on my keyboard to type a million letters I found websites to make all of that easier plus explain it better in videos that I can't do. By the way, it also helps to use talcum powder on the tube, I have some in a ziplock baggie and I simply put the tube in, shake it, take it out and install as usual, the talcum will not only allow easier install of the tire but will reduce your wattage by about a watt or 2, not a big deal but it's something.
View: https://www.youtube.com/watch?v=jvvXrlAUUfU
This video does explain well but that tire was particularly easy to put on. Now I have a set of Schwalbe Marathon Greenguard with wire beads (wire beading is the hardest to put on) I put the tires in my dark colored pickup truck with windows up, and let set getting hot in the sun, took them out after a couple of hours and they were hot, used some Dawn For Dishes (this doesn't matter just any soap will work) and I smeared it on the rim and popped them on with some major hand workouts!
https://cyclingtips.com/2017/12/tips-for-installing-removing-impossibly-tight-tyres/
This next video is what I encountered with my Schwalbe's I mentioned, but I was able to do it without getting the zipties, BUT, if you have an impossible tire, and you tried all the above stuff then this method works wonders:
View: https://www.youtube.com/watch?v=ymvOLOJUVs4
I did have to use a tool called the VAR:
https://www.amazon.com/VAR-Nylon-Tire-Lever-System/dp/B004YJ30M8, this tool is indispensable for tough to install tires plus unlike others of its kind it will fit in a seat bag so you'll be able to put the tire on in case you have flat. This is sort of how the VAR is used but the guy doing it is not proficient at it, but it gives you a general idea:
View: https://www.youtube.com/watch?v=S_-49Pora3I
What he's doing wrong in that video is that you first put on as much of the bead as you possibly can, then do what he's doing, there is no need to use the VAR like he is on the easy sections, it's slow and cumbersome doing it the way he did it. You put on as much as you can, then use the VAR to snap on the bead, in some cases if there is just a small section to pop on you simply place the VAR in the center of the bead area to go on and lift up and back, if it's too large of section then work in small sections from one end to the other. Also notice his hand position on the tool, do NOT grasp it toward the top of the tool or it could snap in two, though it is pretty tough tool, mine is 22 years old and still just as good as new.
Another tool to consider getting is a set of Soma Steel Core Tire levers, these are unbreakable thus you don't have to worry about breaking a plastic tire lever on a tough tire.
https://www.amazon.com/Soma-Tire-Lever-Steel-Core/dp/B001MRYMXQ I've had a set of these also for 22 years (I bought these when I got the VAR), and of course still use them today.
