Terraforming is really overwhelming, and not everyone is as talented as some people who do it quite well, so I understand how they compare their islands to others because that in my opinion is normal, that's human nature, we do compare ourselves to others and their works, consciously or unconsiously, but different people have different ways of coping up to those negative views on their own island...
Those who react as they do are just as valid as people who also compare their islands to others but not really care that much and still enjoy the game regardless, because not everyone has the same emotional capacity as others do, and some people are more sensitive than others...
I hope they are able to cope up, learn to love their own island, and enjoy the game now though, if they still feel the same way towards the game then I strongly suggest for them to turn away on the game as it's not healthy to continue feeling that way...
I also compare my island to others, as I'm also not that good at terraforming, but I still enjoy it regardless because I genuinely like what I'm doing, like I design my island for myself first and others second, so as long as it looks good to me even though it may not look as good for others, I'm already happy with that because I built that and I worked hard on making that area look decent lol...