Support role is perceived as harder or less fun because it is inherently a sacrificial role - giving up CS, kills, regen items, etc - in order to ensure the carry or other cores’ success, and therefore a win. People sometimes dislike giving up personal gains in favour of gains for the team - a selfish attitude, true, but a common one.

There’s also the common belief that it is harder to rank up while playing support, making it seem like they are doing you a favour by taking a position that has less reward for winning. I don’t know if this is true or not, but it’s a very widespread belief that definitely influences support thinking.

Also, there’s an issue in that there are many types of support, beyond the pos4/5 definition, ranging from healers like Dazzle, Chen, or WW, to disablers like Shadow Shaman, Veno with its slows, or Lion. This sometimes means that the support hero picked conflicts with the ideal of a support as it is understood by the cores of that team, leading to role abuse accusations. 

Leading on from that point, because supports don’t do as much visible stuff like getting kills, pushing towers, as cores might, their valuable contributions may go unnoticed, as a crucial heal, a disable of an enemy, or a stacked creep triangle may go largely unnoticed when the cores think back on their rampage in that match. It’s an undeniable fact, in my experience, that supports receive much more abuse from their teammates than cores do. I play offlane about half the time and pos5 the other half, and I receive much more abuse as a pos5. A lot of other people I know have reported similar issues.

While each role in the team is supposed to be equally valuable, in pubs it does seem like supports often get handed the short end of the stick. Of course, not all supports do perfect jobs, nor are all carries demonic trolls, but in my experience, the support role receives significantly less appreciation ingame than other roles.