They speculate the pilots in U.S. are more in tone to the MCAS, the suspected cause for the crashes.
https://www.wsj.com/articles/inside-u-s-airlines-decisions-to-keep-flying-the-737-max-11553092416
Southwest’s Mr. Kelly says his internal, independent safety team was telling him that data collected from the MAX, which Southwest has been flying since 2017, showed no problem. (The airline flies 34 of those planes.)
And even if problems were to occur, Southwest pilots have been briefed on the system that was suspected of malfunctioning in both crashes and have routinely trained on steps to recover should the MAX’s computer mistakenly force the nose down. “These safety-management systems don’t speculate,” Mr. Kelly says.
Southwest, which has the largest U.S. fleet of MAX jets, also completed installation earlier this year of warning lights in its MAX cockpits that alert pilots if the two angle-of-attack sensors disagree, a sign one is failing. A faulty angle-of-attack indicator is suspected of playing a role in the Lion Air crash.