We are changing all the vehicles in the fleet, what with the new regulations and all...
How did that what sneak in there? What is it doing?
The use of what in the expression what with is emphatic:
It is a construction in use in English since the Middle Ages: it means "in consequence of, on account of, as a result of; in view of, considering (one thing and another)". Centuries ago English people also said "What through..." and "What for..." which meant the same thing; but these expressions are now obsolete
(The Phrase Finder)