I just checked on ForeFlight, and the TFR says it is for a 10NM radius around essentially the El Paso airport, and up to 17,999’ MSL. If that were the whole thing, I would lean toward the MANPADs theory. The TFR extending to 17,999’ means that they wanted to leave Class A airspace, which starts at 18,000’, open for aircraft passing overhead at cruising altitude. That, and the 10NM radius would make sense because of the limited range of shoulder-fired missiles.
BUT, the fact that this TFR also includes a separate, fairly large area of airspace right against the Mexican border in a desolate area of southern New Mexico is strange if taking down commercial or other aircraft with MANPADs were the issue.