Your question really should be: "Why do SOME people hate Mojang". To which I would answer: "why do some people hate ANYTHING!".
People hate stuff for all sorts of reasons. Apart from air and water, there's nothing that is universally liked by humans.
Some people hate Mojang because they don't like or get Minecraft, and they are bemused to see the popularity and attention that Minecraft has attracted. Some people don't like Minecraft because it's made by an indie developer. Some people don't like Minecraft because it lacks structure and it takes a while to get going. Some people don't like Mojang because Notch is a heavy-set fellow. Some people don't like Mojang because it begins with the letter 'M', some people don't like Mojang because they liked other studios that participated in MM more, some people don't like Mojang because they irrationally hate everything! And some people hate Mojang because a website told them to hate it.
Some people will always hate something. That's the world. Get used to it. I know I have.
As for why people LIKE Mojang - some people find Minecraft's free-roaming, no boundaries approach to be liberating. Some people really like how Minecraft is like nothing else on the market. Some people like the fact that such a popular game could have been made by a very, very small team. Some people like Mojang because it begins with the letter 'M', some people like Mojang because it's an indie studio, some people like Mojang because they got up one day and said "hey, I kinda like minecraft", some people like Mojang because a forum post or a website told them to like it.
Humans are fickle creatures. No two are exactly alike, and, in case you didn't know, there's nearly 7 BILLION of them on this planet! Yeah! Kinda of lot of people! The actual figure is around 6.9+ Billion, but it's predicted that by the end of this year the world's population will reach 7 billion. If not this year, definitely next year (barring any incredibly horrific events that is). That's 7 billion individual human beings, with different brains, lifestyles, memories, upbringings, experiences and tastes. Point to X and I'll bet my life that I can point to someone who hates X. There is no point to asking "why do people hate X". People have, and always will, hate stuff for no real reason. I STILL can't figure out why someone would hate someone based on skin pigmentation or geographical location, yet loads of people do, and that puzzles me to no end!