Where does it say immigration? You know USBP is bigger than immigration right? Drugs, weapons, currency, illegal goods, etc. Even the largest cateogry of enforcement activity, illegal entry/removal - is itself much bigger than "immigration" which I take it to be people who want to live in the US or seek asylum.

Within illegal entry you have:

  Terror watchlist
  Recycling deportees (commuting to/from construction job sites in Phoenix or coming from Tijuana to do sex work in US)
  Ultralight pilots dropping meth in fields
  Smuggled minors (custody disputes)
  Chinese nationals on the run from China
  Mexican wildlife/hunting violators
  Archaeological and horticultural looters stealing from Sonora Desert
  Dryback US citizens pretending to be aliens to get a free ride on ICE flights to Houston
  US citizen gotaways