Are you saying that weekly long-haul trips are an automatic red flag for US citizens?

Generally they are not -- at least not unless an immigration agent personally finds the multiple entries suspicious. Most of the non-terrorism/no-arrest-pending automated, data-based red-flagging of US citizens relates to customs concerns or concerns about passport fraud/misuse. And the passport fraud/misuse automatic red flags are not triggered merely by number of weekly (including weekly weekend) long-haul trips; that gets triggered only in conjunction with other datapoints.

A lot of trips with the same passport number with same general O/D (i.e., the additional datapoints) will increase the odds of automated redflagging when the pattern is deemed to indicate the heightened probability of passport fraud/misuse (i.e., passport getting person ABC into US, then passport is sent back overseas and person XYZ uses it to get into the US, and so on).