Why do companies change their IT suppliers?

Why do you think companies change they IT suppliers most often?
Because they can’t program?
Because they use old technology?
Are they too expensive?
Or does it all take them a long time?
Or does them speak them Ajut language and cannot speak to them?
Usualy not.

On projects where we came to replace someone
it was always the same or at least a similar song:
does not reply to emails
does not answer the phone
does not call back
not available
does not respond

It’s always been a communication problem.