Because certain people are more interested in dreaming how rich they will become instead of learning how bitcoin actually works.

Every transaction that is included inside a block has a cost involved to include that transaction. Who pays for that cost?
We have 3 choices:

1) Miners are FORCED to included transactions, absorbing the cost themselves.
2) Users are FORCED to included transaction fees to pay for the cost.
3) Nobody is FORCED to pay the cost. Users give an incentive to miners to include their transaction. Miners may do it for free or meet somewhere in the middle, so both pay half.

Bitcoin uses option 3.