The industry standard is becoming Centerlock, mainly because Shimano want it to. As stated elsewhere on the thread, 6-bolt was the original standard, however Shimano then launched their own standard - Centerlock. They own the patent: https://patents.google.com/...t/US20070240945A1/en

As a result, Shimano are incentivised to ensure that the industry moves across to CL, something they've actively encouraged by only offering their high-end (Ultegra / Dura Ace) level rotors in CL, not 6-bolt. Given they're by far & away the leading OE supplier of road groupsets, hub manufacturers have been forced to switch to CL.

Interestingly, the graphic below shows why 6-bolt is arguably the superior design from a hub designers perspective - you can increase the bearing spacing on the axle as shown. However, it undeniable that CL is far superior from a user perspective when fitting, aligning & changing rotors.

Edit: can't get the graphic to work, link here: https://ibb.co/WKPLpfT