At the risk of sounding like a broken record…
Weight is a problem, and many recent U.S. passenger locomotives have been very heavy for 4-axle locomotives. But there are two distinct issues to consider. Reducing over-all weight probably makes things a bit more energy-efficient (less mass to accelerate), but for safe operation at high speeds without damaging the track with "hammer blow," weight per-axle is, I would guess, just as important. So, given that American railroad operators seem to be very cautious and conservative when it comes to choosing engines, and given that they like the tried-and-true, comparatively low-maintenance, but heavy, engine designs from EMD and GE… WHY HAVEN'T WE SEEN A REVIVAL OF THE A1A TRUCK FOR PASSENGER POWER?