It’s also not fair to buy a thing for a cheaper price because the IP rights aren’t included, then try to cut out the IP holder when things need fixing. The company bid a low initial price betting they would get additional revenue on spare parts and change orders later.
Finally, the military has incredible leverage at the start of a program that they could use better. Companies will include IP rights if the alternative is not getting a contract at all. Once the piece of equipment is fielded, leverage returns to the company.