"Too many" entries by a US citizen back into the US must be quite a bit. Weekly (including weekly weekend) long-haul trips are not an automatic red flag.

The number of "too many" entries into the US by foreigners coming into the US under the VWP is probably a lower number -- lower than for US citizens re-entering the US -- given all other factors being near-equal, but even that is not an automatic red flag unless it appears to be a violation of entrance conditions.