why did Celebrimbor allow Sauron?

[Galin]

This also hails from the Unfinished Tales text titled Concerning Galadriel and Celeborn...

'Now Celebrimbor was not corrupted in heart or faith, but had accepted Sauron as what he posed to be; and when at length he discovered the existence of the One Ring he revolted against Sauron,...'

It is also said (same text) that Sauron had better fortune with the Noldor of Eregion '... and especially with Celebrimbor, who desired in his heart to rival the skill and fame of Feanor.'

Noting too (and in any case) CJRT's explanation that a section of this text was emended to the later story that made Celebrimbor a descendant of Feanor.