One big reason the "GOP Establishment" is behind Loeffler is that she's very wealthy and can finance her own campaign. This is a huge deal for this particular Senate seat because the GOP has to prepare for two elections in the next three years. This 2020 election is just to serve the remainder of Isakson's term. That term ends in 2022, so whoever wins in November will have to run again two years later.
That's why smash-mouth plays like Doug Jones/Roy Moore and the Ted Stevens Take-out actually work for them.
Meanwhile, we have Keating Five McLame, Pierre Delecto and The Weak Sisters.