Turkey's only in NATO because they were the only European country at the time that had a geographic border with Russia.

Originally, Turkey's intention for joining NATO was to obtain a security-guarantee as the threat of USSR invasion was looming after WW2. Turkey's initial bid was rejected, and they only received "defense cooperation" after submitting their second bid alongside Greece. It was after Turkish president Celal Bayar expressed the fact Turkey sent troops to fight for South Korea in the Korean War that NATO fully accepted Turkey into their alliance. Later on, the U.S. would build bases in Turkey that would house U.S-controlled nuclear weapons.

Reasonably, Turkey had good reasons to join NATO at the time. It's shameful that the coin's flipped now that the Turkish government is run an asshat who would be ready to jump ship alongside Putin if things don't go his way. These days, Erdogan throws a fit for anyone harboring any kind of affiliation with the Kurds. Such as:

• Denying the U.S. from arming the YPG in Syria (yes, they managed to block the America from doing the most American thing possible: giving out guns to foreign entities)
• Being the only country to veto Sweden & Finland's bids to join NATO for harboring members of the Kurdistan Worker's Party, which Turkey designates as a terrorist organization. Going as far as to threaten NATO with leaving the alliance if Sweden & Finland don't adapt their laws to be more in-line with Turkey's "security concerns." (Desire to genocide Kurds)