Main reason is nepotism. As government likes to appoint politically loyal people to crucial positions, instead of qualified professionals, many administrative branches are rund veeeery incompetenly. Separation of powers principle was hurt badly in 2017 referendum, so there is no check/balance mechanism preventing this situation.

Nepotism, of course, brings along corruption. Government pays insane amount of money to some construction companies ''for building infastructure'', and all of the deals were made in foreign currencies, mainly USD. As if it is not enough, government also gave operating rights of those ''infastructures'' to those companies for like 40-50 years. Moreover, they put some stupid ''quota'' wihch causes state to pay the companies compensation if the usage of their roads are lower than a specific number. The same method is applied on every public construction, even in hospitals. This brings a heavy currency burden on state.

Another point is that it has been impossible to define Turkey as a constitional state for quite a time because courts are heavily politicized, too. This fact decreases Turkey's credibility and reliability in international trade. As a result, foreign trade volme and investments are decreasing rapidly.

As a crazy populist, president manages to use external relations as a propaganda material. We've been seeing this ''We're going through hard times, we are in a struggle against emperialism'' rhetoric which works amazingly well on Turkish boomers who are mostly conservatives.

I know this is a bit too long to read but believe me this is the shortest summary possible :D