No upgrades in speed tiers in 4 years

I was one of the very first dsl customers to switch to uverse in my area. Back then the fastest speed tier was 24 down and you had to be very close to the vrad, I could only get 18 down. I have read about all the upgrades they do now like different cards and different frequencies and see 45mbs advertised on tv all the time. My question is why in 4 years has no upgrades been done to my service? I check monthly on myatt.com on the upgrade speed and 18 down is always the fastest available to me. Can someone please let the right people know I have been a loyal customer for a very long time and im interested in very fast speeds? Thanks in advance.