OK, I’ll bite. It is a mixture of reasons that appear to include: (1) they are cuckolded, fearful, low-self-esteem losers at heart but have gotten elected so need the pretense of appearing important and above it all to feed their puffed-up-yet-pitiful egos (aka they are not real and can never fight); (2) they don’t know because they are too self-absorbed and clueless to even notice their environment with garbage like SPLC in it; (3) they are told by their so-called “leadership” what the talking points are and those never include anything as basic as pushing back against a lying/manipulative MSM; (4) they never had any principles or fundamental beliefs anyway so SPLC sounds just as good as the next thing out there ; (5) they are compromised in several ways with carrots such as cash/insider trade deals or sticks such as bribery material to be withdrawn/used if they speak out boldly and directly about this vicious SPLC hate and money-laundering scam or anything else that rocks the boat; and/or (6) they aren’t very bright (IQ < 100) and won’t be able to comprehend the obviously successful path that Bannon, Cernovich, et al. are showing them.
My hunch is that any individual Republican who is silent or indifferent to the outrages of SPLC has one or more — maybe all — of these traits and circumstances.
Rule of Thumb for any elected official: the only thing this person had to do to achieve their status/job was to get elected, which in essence is a mass marketing operation. Nothing much else beyond this is required to be a politician, hence, with such a low bar for success, we can never have excellent/top-tier representation. The exceedingly rare exceptions prove this rule.