What is the reason for this? Do people abuse it?

I've relocated from YYZ to MCO and am AC*G but will be flying UA in 2015 and flew them a lot in 2014 but earning on AC Altitude program to ensure I wouldn't orphan miles. I wrote MP to ask about a status match and they said, "we do not include Star Alliance airlines in the Premier Status Match promotion." I'm struggling to see why they wouldn't be motivated to try and get my business provided I can demonstrate loyalty in the beginning of 2015. I really only care about extra bag allowance and lounge access.

From other threads it seems the only option is to earn miles with your new program (MP for me) and hope they accept your gold status card in your previous program (AC*G for me) for bags and lounges.
See: http://www.flyertalk.com/forum/star-...s-another.html