At least in the US, some of it is the vagaries of government acquisitions. The requisition process is one that works fairly well for services and products that

At least in the US, some of it is the vagaries of government acquisitions. The requisition process is one that works fairly well for services and products that are established and largely interchangeable, but is more difficult for something that's either emerging or complex. So it's fairly straightforward to say "I require a piece of construction equipment that does something" and then go view a few off-the-shelf options and pick the best price. But for software and services, especially things that don't exist, the existing requisition process doesn't work well. You're required to plan very far ahead in a market that moves quickly. By the time you get to bids, the requirements have likely changed, but it might be too late to go back and change requisition without going through an approval process again. It also requires you boil down a process into a series of atomized pieces that can be scored so you've got a clear paper-trail of the acquisitions process. It's a system that benefits vendors that can manage the red tape that's there to prevent corruption.