No joined up thinking at all
Individual government departments each seeking to save a few bob off their own budget; whereas, maybe for a little more, they could 'buy British' - which creates jobs, etc, in the UK that DO pay tax, that DO build up UK expertise, that DOES make them better able to complete internationally, that DOES keep British data within our borders, ...
Overall a few different choices ends up benefiting Britain overall.
But politicians won't do that: each trying to bring their departmental budgets down and, anyway, the benefits of beefing up British business probably won't be noticeable until after the next election -- so they don't give a toss!