You guys are amusing, talking about these guns as if they are useless antiques.
They will still do everything they ever could do, and better than most "modern" plastic pistols.
Sometimes progress isn't what you think it is!
I own two 1911s, and I agree that they're great to shoot. Anyone who's ever shot one would agree after one or two mags.
However ...
Personal/enthusiast ownership and organizational ownership are two different things. A 1911 is a very old design, and the tolerances are loose compared to a modern pistol. In a large service inventory, they require lots of labor (meaning tinkering and hand-fitting) to keep going, and parts don't necessarily swap from one example to another as well as you might expect. Plus, the field-stripping procedure, compared to that of a modern pistol, is just absurd. (A 1911 breaks down into eight parts, double that of a modern gun.) I'm surprised guys in the field don't drop and lose some of the small parts (barrel bushing, slide stop, recoil-spring plug), without which the gun won't go back together operate. That probably actually happens.
All this is time-consuming and expensive. The idea of financing this with taxpayer dollars makes no sense, not in the 21st Century. And the U.S. military didn't adopt the M9 purely to transition to NATO-standard ammunition; they could've switched to 9mm 1911s had they really wanted to. They switched in part because the 1911 design was old, the inventory was rickety, and they needed a modern, high-capacity firearm. (The M9's breakdown/reassembly is a snap compared to that of a 1911, even without a captive recoil spring.)
I don't personally have experience with a Hi Power, but I suspect, from an organizational perspective, that most of the same realities probably apply.