Because it is a magnet wrapped in a certain number of turns of a certain gauge wire then encased in the plastic shell.

Yeas ago ( 60's, 70's ) when I was in the field servicing computer equipment, some of it had these but they were then called 'reluctance heads'.
They were used for the same purpose, generating pulses to tell electronics how fast something was turning and what the current relative position was.
They were like a threaded bolt though, you could adjust them to a certain distance from the spinning 'reluctor'.
I never did know why, but sometimes they would just fail to send a signal of sufficient strength to work correctly regardless of adjustment and would have to be replaced.

We have 4 more of these, the 'tone' wheel pickups for the ABS, they don't seem to fail with the same frequency as the CPS.
I do still believe however that the connector to the CPS is a large part of the problem in that it either does not provide sufficient contact on the pins, or is prone to corrosion due to it's design.