Why does the military and police use the MP5 and HK UMP when the higher caliber Thompson SMG is still here?

The military doesn't use MP5s, probably contractors do but that's because they suck. The SWAT uses MP5s, considering the fact that they work at close quarters. The military uses M4a1's and M16a4's, because they are very proficient and reliable rifles. Thompson!?!?!? Really!?!?!? That thing is ancient! It may have .45 ACPs, but you have to look at the gun and not the bullets. It's very very very inaccurate, therefore rendering it useless in modern combat (plus you can't really place any useful attachments on it).