The answer is that your expectations are off. It sounds like you flew CO as Plat some years ago. Upgrade rates have been dropping drastically for everybody, even Plats on high fares, and there are plenty of Plats reporting low upgrade rates. If you want to travel in front with a high degree of certainty, pay for first. If you're happy to be upgraded sometimes, buy the cheapo coach fare (I class is pretty low, much of the time this is the lowest O/D fare offered on BOS-IAH) and chance it. Or try another carrier (as a US 1 you presumably have an excellent upgrade rate; the problem is that you have to fly US to get it).

I managed 3/17 upgrades on CO as Gold this year, all of them on BOS-IAH, so actually this is not such a bad route - if, like me, you are prepared to fly at 9am on January 1, or 11am on Tuesdays...

(And I'm ignoring the OP also... )