Why must he do that before the Ethics Committee investigation, which has already begun, is finished? That's like sending someone to prison before the trial is over.
The people who resigned did so "voluntarily." Franken has the right to hang in there, as has Moore. Lauer and Rose were booted by private companies, which is a different ball of wax.
Investigations are things are are done to find out what is not known. Franken's misdeeds (crimes) are AlREADY known.
Having an investigation over what is already confessed to (with photographic evidence to boot) is a FARCE, and is obviously being pursued only to keep Franken's Senate seat Democrat. Shameful. Around the world, they must be shaking their heads. Disgrace to America.
And no, the politicians did NOT all resign voluntarily. Murphy was prodded by Paul Ryan, with Kihuen, Pelosi demanded his resignation, and some others paid out hush money (ex. Blake Farenthold - R-TX)