MPLS latency increase explanation

Hi r/networking,

I'm quite a novice however I have a question regarding MPLS routing. I often have to explain to clients who provide traceroutes that a latency increase to roughly 135-150ms is normal when the hop is via MPLS, however I'd like an explanation myself as to why this is. An explanation as basic as possible would be appreciated, as I'd like to provide this information to clients who bring routing issues to us where possible.

Thanks everyone!