I just calculated my reward using various mining calculators like whattomine/cryptocompare/coinwarz.
All show me that I am gonna get my investment back in about 6 months.
If I buy 1000 MH/s from any reputed miner then why shouldn't I be profitable?
Do they hide anything from me?
It can be profitable. It can be not profitable.
1) look into the contracts. Is there a fee for electricity/maintenance etc. -> did you include these into you calculation?
2) how long is the contract?
3) there will be difficulty changes. The more profitable the coins are, the more people want to invest, the faster the difficulty will rise, and profits going down. There is no mining calculator which can predict this behaviour exactly.
4) there will be price fluctuations. Every coin is very volatile.
You can be sure that almost every day your daily profit is getting less and less and less. When there are fees, then there is a big chance you will reach the point that your profit is lower than the fee and mining will be ended. When there are no seperate fees, the mining period is short (1 or 2 years max)
In this case I guess it's a 1 year contract. In my calculations, when I have to get 6 months of today's profit to reach ROI, it will take at least 1 year in reality to reach it. So you see the point?