travel or counter-terrorism measures since 2000? Why would a ~3 day bus trip take 6 months? Getting a visa to the US from a rebellious part of Yemen, let alone multiple shouldn't be a walk in the park given, you know, that that part of Yemen is shooting at people.
And what does who gets asylum have to do with people sneaking across the border? Asylum seekers are fine with getting caught if they have reasonable expectation of getting asylum. Fine - but seeking/getting asylum is not a prerequisite for getting into the country and/or moving around it (whether for economic reasons or nefarious reasons). Getting in without getting caught OR taking advantage of the delays in processing are both opportunities for risk.

ABC story: "More typically, nonresponse or bureaucratic obstacles make returns difficult, if not impossible," global migration researcher Erlend Paasche wrote in a 2022 report. "If, for instance, the U.S. government approaches an origin country's embassy to request assistance in verifying identification and issuing travel documents as part of a removal, that country has various tools at its disposal to complicate the return."

With exceptions like Iran, it is relatively rare for countries to outright refuse to take back their own citizens, according to the Migration Policy Institute.

But China and Russia have been listed by the U.S. as two of the least cooperative countries when it comes to verifying and returning their would-be deportees. Other uncooperative countries include Cuba, Eritrea, Hong Kong, India, Iran, Iraq, Laos and Pakistan.

Countries can choose not to respond to U.S. requests or impose high bars for identity verification, making it difficult to prove the deportee's country of origin, according to Paasche.