Again, there is equipment that Pemex cannot get access to.
Pemex is no better than BP or Exxon when it comes to pollution. They have had some horrible accidents.
Not all the oil companies that were nationalized in 1939 were American, nor were those that cheated, stole and polluted did so because they were American. Shell is a Dutch company, and there were some other European companies that no longer exist that were also nationalized.
Oil companies are generally bad citizens because they are oil companies the nature of the business breeds deceit.