That doesn't add up, the 7.62x25 Tokarev predates the Soviet Union, ...
No, it doesn't predate the Soviet Union. The "October Revolution" that created the Soviet Union happened in 1917.
was largely replaced by 9x18 Makarov as of the 1960s, and the Soviet Union had already collapsed by the point that NATO started looking to adopt a new cartridge.
The official dissolution of the Soviet Union was at the end of 1991. This changed nothing concerning people opinions about the Soviet created 7.62x25 Tokarev.
Furthermore, they were already using 9mm Luger which was a German Cartridge, so if they were just against using a cartridge used by a former enemy force, then why did they ever adopt 9mm?
What you're missing here is that Germany was part of NATO, since the founding of the organization, and despite the fact that, in the past, they had been enemies, with NATO, Germany was one of the members, no longer a former enemy. All one big happy (or not so happy) family, now...
SO, adopting the 9mm was adopting one of the member nation's rounds as the standard.
Also, I'd like to think that they're not so petty that they would sooner waste time looking for a whole new cartridge just because an existing cartridge which seemingly already suits their needs just so happens to have originated in a nation whom they were once in conflict with.
You'd like to think so, but history has shown that they
were that petty, and I'd bet on many issues, they probably still are.
A lot of people had to work very hard inside NATO to overcome each member nations's version of "not invented here" syndrome. Originally, NATO countries didn't want the US 7.62x51mm round. Eventually the deal was struck that they would adopt it if the US adopted their 9x19mm pistol round. A few short years later NATO was VERY upset when the US changed to the 5.56mm, and expected them to follow suit. The eventually did, but weren't happy about it.
The 7.62 Tokarev round was never popular or even really available in the US until after the fall of the Soviet Union. And, after that, it was really only available in former COMBLOC firearms. And, also only FMJ ammo was common.
Essentially it was a milsurp round of interest only to some collectors and to people with very limited budgets because for a while the guns and ammo were dirt cheap.
That is no longer the case, there is no evidence of consumer interest sufficient to justify new firearm designs in that caliber, and so the circle closes. its not popular because there are no new guns and ammo, and because there are no new guns and ammo its not popular....