The way it works is he is paid a salary by the university, but he must attract grants in order to pay for research and staff. Likely he is managing several large grants. When I say 'managing', I mean there is an administrator and they collaborate on how the money is deployed, with many stipulations which were part of the grant application.
His university will be judging his success or failure based on how many of these grants he can get, how big they are, and their 'impact' - so he has to travel to collaborate with others so they can apply for grants as a team, he has to travel to the places where the impact may be most useful. Whatever detractors say, research which moves us forward is still an international activity. In Britain there's still a whiff of colonialism about it too.
The point is, it is not the university's dime that's paying for the travel. We as taxpayers do not generally pay for travel and accommodation. Grants pay for the rooms that are in use, even! They pay for equipment. We aren't even paying the salaries of a lot of research staff. It all comes from grants with various foundations (and yes some government research councils as well).
People have less than zero idea quite often of how academia is organised. Please don't believe the Daily Mail, Reform etc. University staff have been cut to the bone, actually, and where you might have got subsidised accommodation and a secretary and long holidays, that was about 70 years ago and it all gone, replaced by a far more corporate culture. Fair enough in some ways but it really is not a dreamworld by any means.