Opt-In doesn't help them achieve their product goals.
Triplebyte as founded isn't working so they're trying to take a valuable asset they have (engineers looking for jobs) to compete with linkedin
The problem with bootstrapping a linkedin competitor is the same chicken-and-egg problem with networks generally. You need people on it for people to join it.
What Triplebyte wants is your identity public. That's the product goal. The problem is that opt-in won't get them that. What are the incentives for anyone to make theirs public?
How many people who were searching for a job without telling their company are going to opt-in to make that public?
Most certainly not enough to bootstrap a LinkedIn competitor.
So someone had the idea to move fast and break things, either:
a) hoping no one would notice
b) hoping the fallout wouldn't be bad
c) not caring that the fallout would be bad
d) not knowing that there would be fallout
none of the above are particularly inspiring. It does seem hard to miss this coming