please correct me if I'm wrong, there are two suppliers of those probes. Only one of the suppliers probes obviously may have a problem at times, that's why upgrades are available,...
So while its fine if an airline can chose powerplants, if I were an aircraft OEM, I would limit myself to one supplier and one model of such probes.
You're quite correct. There are multiple suppliers, however the aircraft manufacturer owns the design. Probe vendors are given the drawings and manufacture to the aircraft manufacturer's design specification.
To complicate matters further, there are in addition, approved repair stations that can "repair" a probe that has been eroded out of specification or where the heater has failed. They don't actually repair the probe at all, they rebuild it to the original drawings but at a lower price than the original probe manufacturer charges for a brand new replacement.
The result is not a PMA part, it comes back with the same Part Number and Serial Number as the probe that was sent for repair. A bit like restoring an old aeroplane using nothing but the original data plate.