"....so does that mean 132 chose not to opt in - it isn't just me?!)"

A few possibilities:

Maybe number of shares is so few not worth the bother.

Some may not know about the opt-in availability.

Some may be buried in inheritance issues.

Dead investors took the shares with them.

Some don't want to opt-in (Not 132)

Any other possibilities gang?

You cannot claim 132 made a choice not to opt-in. Low probability.