There's very little interest in the domestic passenger loco market because passenger systems are so sparse in North America that the unit quantities suck for developing any kind of manufacturing scale. All of the big rolling stock vendors (Siemens, Alstom, Stadler, etc.) have Euro diesel, electric, and dual-mode locomotive families that could be adapted for the North American market. Siemens, with the Vectron family (which the Charger was derived from) was the only one that actually tried to break it here. And they got lucky, winning the huge Amtrak order to establish some manufacturing scale and then perpetuated it with enough follow-on orders to keep their factory constantly going. Stadler just won a large battery-diesel hybrid contract with VIA Rail that'll set up a Canadian manufacturing plant, so they're sort-of in the game now (albeit not at Buy America-compliance). But unless they immediately offer a straight-diesel version I can't see them getting any follow-on orders, because their battery-diesel hybrid make is as stupidly expensive as the Siemens B+AC batt locos while still having diesel emissions. I guess the Bombardier/Alstom ALP-45DP dual-mode is also still around as a new-buy option, although only NJ Transit seems to like that one; the manufacturer also never bothered to market a domestic straight-diesel version. The rest of the worldwide vendors have sort of held their nose at it. And two huge American vendors that dominate the worldwide freight market, Wabtec (ex-GE) and Progress Rail (ex-EMD), don't make any passenger locos whatsoever because the economics of it suck so much compared to just pumping out hundreds of freight units per year. They instead subcontracted their technology to third parties to develop passenger makes: which resulted in the extremely unreliable F125 (EMD-Caterpillar-Vossloh joint venture) only bought by Metrolink and the HSP-46 (MPI-GE joint venture) only bought by the T. Both have been withdrawn from the market (with the HSP never advanced for Tier 4 emissions), despite using prime movers that are in widespread use in literally thousands of freight units in America.
It's not like the Chargers are perfect, either. They have problems in snowy weather with the fans inhaling snow into the engines, which is why VIA Rail went with the Stadler hybrids for its long-distance procurement. And the Amtrak Midwest SC-44 Chargers took an unusually long teething period to work most of their bugs out, and are still somewhat hated by Amtrak engineers on RR.net because of their finicky computers. Something with higher incumbent reliability would definitely get fairly considered by buyers here. But nobody wants to build for such small and intermittent unit quantities when that makes equipping a Buy America factory a futile venture. There used to be a robust rebuilding market for older power, which is why the F40PH lasted almost 5 decades as the continent's #1 most ubiquitous passenger power. But rebuilds top out at Tier 0+ emissions compliance, while most federal grants sources will only pay for Tier 4's that can only be bought new. Hence, the Charger becomes the literal only practical buying option. The situation is not likely to change soon with so few non-Charger users left who have an identified need to buy new units in any sizeable quantity.
Much like bus-land being whittled down to somewhat checkered-reputation New Flyer and just a couple others for Buy America-compliant builders of any scale, it's a sign of a deeply dysfunctional domestic market meeting deeply dysfunctional regulations (i.e. Buy America being an utterly failed program) that you simply can't get the product over here. The product exists! Hell, it's being built in America by American companies every damn day for freight use! But the economics are so uniquely fucked that no one except Siemens...and only because they captured lightning in a bottle...is building the passenger versions here.
