Money talks. The donor class needed 8 dems to end the shutdown and turn on the money fountain again, and they got them. If they had needed 25 dems to cave, they would have gotten 25. If it was (somehow) critical to maintaining their wealth that 40 republicans vote for the "Trans and Immigrants are Actually The Best Bill", then 40 republicans will vote for it. Congressional outcomes have nearly nothing to do with voter preferences, you can look up studies on exactly how that has become totally desynced the last century, especially since Citizen's United.