Some great suggestions!

Keep in mind that some runners are out looking for an edge; that and cyberware installations are much more common procedure in the 2070s. If your job today required that you get a datajack to access the network, would you do it or get another job? That of course doesn't cover the extreme cases, but while much of the modifications started out as medical replacements, Corps found that there is good money in just talking someone into it. And just like many addictions, once you start...

I think the initial reason for getting cyber is the most key, after that, it is an excuse to "be better" or "I've already gone this far".
* burned out mage looking for a replacement for their loss
* gang initiation; to get in you have to get something installed (usually second hand of course)
* survivor from a meeting with Tamanous - most people wouldn't make it...
* it was in your contract with 'XYZ' corp or 'ABC' security organization
* for the rush; kind of like starting tattoos or body mods
* believe (sometimes fanatical) in transhumanism --- already groups doing it today!
* getting old; doing something to feel young again
* character needs a sense of power and has chosen the cyber path
* once part of a religious groups that worshiped "the machine"
* Renraku Arcology shutdown survivor - may or may not be the lucky one...
* Pro sports player (probably out for some reason, or maybe runs for the rush); cyber is allowed in some sports leagues; probably even required in others!
* research candidate - "We'll pay you if you let us..."
* organized crime enforcer
* worker from an extreme environment - deep sea, desert, arctic, toxic etc.
* corporate espionage agent
Just a few thoughts!