When we would send up Canadian reserve units against US active units, we found they had no idea their people would pass out inside the combat vehicles and tanks from extreme heat and dust, or deal with optical illusions from heated air, making it easy to trick them into going into tank traps that were covered by snipers with heavy and light mines. Or what happens when rocks crush your tank in a mountain pass because you fired your main gun next to an unstable rock face.
Sims only work so much.
You have to train for the bad things that happen, like your tank getting stuck in loose soil with water, and people who are actively trying to make you do the wrong thing. That requires actually taking vehicles into those actual types of terrain and obstacles.
And you know what? They do. The US and Canadian military often train together in real life simulation training. There are also many cross-branch military exercises for doing this.
Yes, simulation only goes so far. But real life training is very expensive - there's a lot of logistics involved (you have to invite over allied countries forces, plan a date, plan the scenario, etc), so you only can hold them every few months. And the larger the engagement, the less you can hold because the logistics make it too damn hard.
So there is real life training, it's just harder to achieve due to time, money, manpower, scheduling and a whole piles of other factors.
Digital sims are good for re-enacting hard scenarios (flight sims have the worst quality airplanes designed - something about them is always failing and it's rare to have a flight go uneventfully). It's also good for just getting up and going - in flight training, there's a strong push to increase simulator usage because they're a lot cheaper to rent (some schools rent them for free and allow student pilots unlimited usage to practice), and schedule than an airplane. You can also get a lot more done - if you want to practice landings, you may only be able to do 6 or 7 in a real airplane because you're working around other traffic, but in a sim, you can shoot dozens or more, and you can even repeat the same environmental conditions (bad crosswind? Well, every one can be a bad crosswind!).
Real life tanks cost a lot of money to operate, simulator tanks are much cheaper and can be run often without much permission required, so the keen soldier can re-run scenarios without needing to get a whole pile of approvals (and missing crewmembers can be simulated, too).
Yes, sims aren't perfect, which is why the miliary runs real life exercises too, but those have their own limitations, especially when it comes to building up experience because you can only run so many of them.