Here's my take on it. And sorry for sounding like a dick earlier.
We are competing head to head with many of our regional "rivals" for the chance to host a regional. If you look at the RPI matchups of the past few years, A&M has a TON of top 50 and a TON of top 15 RPI matchups, while TCU, Rice, tu, (etc), struggle to get those because of their conference play. Granted the Big 12 was pretty damned good last year, but they are usually fairly top heavy, with the bottom of their league being crap. Even with the Big 12 being good, A&M still had twice as many top 15 games played as the next (tu).
So the logic goes that if you play them in 3 game series, it gives them 3 more games to play a top 50 (top 15) team (which, if they win, then that could be the tie breaker). Even if they lose, it'll more than likely give them a bump on the RPI (TCU not withstanding because they're usually top 15). Why give them that chance? It helps them out of playing in a weak conference while we have to sludge our way through the SEC. The numbers below will show y'all what level of competition we're facing without playing the regional teams. A&M is not really competing with the CS-Fullertons, Pepperdines directly for chance to host a regional.
I'm not factoring Top 15/50 records in because I think they're irrelevant to this discussion. It's more about creating opportunities to impress the committee.
So, yes, the Big 12 really needs the RPI bumps more than A&M does. It just doesn't make a whole lot of sense to A&M to give these teams the opportunity to "overwrite" conference opportunities. And while it does create series that have sentimental value to some fans, it doesn't add any post-season value (which is the name of the game). Plus, as others have said, it most likely takes away a home series every year.
Here's the breakout (using Warren Nolan's RPI and regular season/conference tournaments only). We'll go back to 2013, the first year we joined the SEC.
2016
A&M - 18 Top 15 (All in the SEC), 33 Top 50, 7th SOS
Rice - 6 Top 15 (None in Conf USA), 31 Top 50, 15 SOS
TCU - 3 top 15 (all in Big 12), 24 Top 50, 23rd SOS
tu - 9 top 15 (8 in the Big 12), 18 top 50, 34th SOS
Tech - 5 top 15 (3 in Big 12), 27 top 50, 22th SOS
Baylor - 7 top 15 (all in Big 12), 15 top 50, 27th SOS
UH - 3 Top 15 (none in AAC), 23 Top 50, 68th SOS
2015
A&M - 6 Top 15 (All in SEC), 28 Top 50, 23rd SOS
Rice - 2 Top 15 (none in CUSA), 11 Top 50, 48th SOS
TCU - 4 Top 15 (None in Big 12), 22 Top 50, 38th SOS
tu - 3 Top 15 (all Big 12), 16 Top 50, 73rd SOS
Tech - 3 Top 15 (all Big 12), 13 Top 50, 70th SOS
Baylor - 8 Top 15 (4 in Big 12 - Also played A&M and LSU in MMC), 15 Top 50, 36th SOS
UH - 2 Top 15 (none in AAC), 25 Top 50, 32nd SOS
2014
A&M - 14 Top 15 (12 in SEC), 34 Top 50, 8th SOS
Rice - 9 Top 15 (none in CUSA), 22 Top 50, 12th SOS
TCU - 10 Top 15 (7 in Big 12), 32 Top 50, 17th SOS,
tu - 11 Top 15 (7 in Big 12), 42 Top 50, 2nd SOS
Tech - 14 Top 15 (8 in Big 12), (30 Top 50, 9th SOS,
Baylor - 12 Top 15 (11 in Big 12), 33 Top 50, 7th SOS
UH - 6 Top 15 (None in AAC), 37 Top 50, 15th SOS
2013
A&M - 16 Top 15 (12 in SEC), 32 Top 50, 10th SOS
Rice - 1 Top 15 ( none in CUSA), 9 Top 50, 82nd SOS
TCU - 3 Top 15 (none in Big 12), 12 Top 50, 61st SOS
tu - 0 Top 15, 10 Top 50, 36th SOS
Tech - 0 top 15, 12 Top 50, 35th SOS
Baylor - 3 Top 15 (none in Big 12), 17 Top 50, 30th SOS
UH - 0 Top 15, 10 Top 50, 103rd SOS
As you can see, A&M consistently has more top 15/50 matchups and a stronger strength of schedule. Playing the regional teams would just give them more chances at tiebreakers when determining regional hosts. This is a big factor in the committee (politics notwithstanding). As is records, but this thread isn't about hosting qualifications.
Again, that's my take on it...someone else may have a better insight/opinion on the situation. I might not have explained it very well.
TL;DR - it doesn't add any RPI value to A&M, while it gives a regional team in a worse conference the chance to "overwrite" conference level of difficulties.