Because the state once privatized the single biggest national interweb infrastructure and did so without concluding what we call a "goodwill agreement", which is essential to make sure the overtaking company does offer quality service to citizens.
Currently, Turkish Telekom holds the entire ADSL infrastructure with no alternatives. There are alternatives but they operate by leasing their own portion of TT's national infrastructue. In this case, we are talking about a monopoly. The TT fuckers are almost the single choice we have. They are partly an interest group with close ties to the government and imposing a valid sanction on them through consumer complaints is a bit impossible as well. In the end, their offer is kind of "take it or leave it".
Even now the best connection option one can get here comes with approximately 8mbit. After downloading 50gb, your speed is throttled down to 3.5mbit for the rest of the month. Interpretation: We still have bandwidth-capped connection like a third-world country. On top of that, TT requires you to have a native phone line in order to get internet connection. That comes with an extra of 19 TL for a service you never ever use. A bullshit option is to leave aside the phone line connection under the "Plain Connection" package. When you get that package, there is no longer a phone line but still an extra 15 bucks to be paid for preferring a "plain" connection xD
Not to mention if you want to get parallel download/upload (can't remember the exact term for this) or good speed without a quota, you are supposed to pay a shitton of money. After paying that much, one would probably be too sad to even think of downloading shit.
On the other hand, we have fiber internet companies (2 of them atm). They offer fast connection through their "own" infrastructure. But this time around, if you want to subscribe, you need to be living in a housing complex where a bunch of others in your condo are also subscribers. Afaik, they are required to install a small substation to the building and it certainly comes with a cost. That is why they would like more than a few subscribers to get you going.
In conclusion, we are royally screwed with no choices. The only choice we have is off the leash and can fuck consumers as desired. No sanction there. Just another field of service where the current government has abandoned citizens to their lousy fates.
Hope this is explanatory enough. I can still write walls and walls of text, if you want me to.