The problem with forcing a real filibuster is that it's harder on the majority who want to break the filibuster than on the minority who want to keep it. Filibusters are kept going by all kinds of procedural devices as well as by pure talking. If you're going to break the filibuster, you have to keep enough senators on hand to respond to quorum calls and such, to force the minority to cave through exhaustion, and in the meantime your side gets tired too, and you need more of you than there are of them.

This is why real filibusters were given up, and the "virtual filibuster" invented instead.