There are reasons to keep it a B Tier.
Players MUST be a PDGA member to play in an A Tier for one reason. I am sure there is a good number of people that play every year that are not a current member of the PDGA.
Secondly, the PDGA will also collect $1 more dollar from each player (it is $4 for an A-tier per player) so for example, that would be nearly $100 from the pro payouts.
Lastly, you request a date from the PDGA for a date for an A Tier and then they give you one. If the MDGO does not get the Memorial Weekend date, then what?
A Tiers are typically set up to be regional events. This event is pretty much closed to Michigan players only for the most part so it does not meet the regional feel of an A Tier.
It is a huge event already and I personally don't believe that it adds to the event if it is an A Tier...