Too much hype, low to no upgrade to the project.
I guess the fact that they are very slow in terms of making some upgrades to their projects is the reason why they are being hated, but TBH I can't feel the hate on the project... or it's just because I'm not following the project that much.
. Maybe another reason is that, they are saying that they are the "Ethereum Killer", but developing very slow, and like others said here, they are overhyping the project too much, but the progress is very slow.
Still, Cardano is one of the top tokens right now in terms of market cap, and it has been there for a very long time. It just shows that there's a huge community behind it. I'm currently holding, and staking Cardano for almost a year already, and it's always good to earn coins just by doing nothing though I'm thinking of selling it already, and purchase Ethereum.