Why is Turkish Air no longer an option for air travel?

[mikehutchison]

Looking to understand why Turkish Air is no longer an option.  They have much better flight schedules and prices than the airlines that are currently available.

[stevecroft]

They are available through Travelport agencies/TMCs

[cberndtsen]

TKs contract expired with SABRE and this is why - if the GDS you are using is SABRE - you can not book them through the tool or with the TMC.