Basically (!), it was funk that killed the organ bass pedal player... Most music up to them was reasonably easy to play on pedals. In fact, most bands appreciated the bass part being simplified and cleaned up a bit by the limitations of what you can do with your feet.

But slapping and popping changed all that, and made copying contemporary pop a lot harder for the pedal guys. So it started to die out.

Funny thing is, a LOT of modern pop has got some pretty dumb, simple basslines (the poor kids today think it is OK to just whang away on repeated eighth notes all night long!), and playing them on bass pedals is a doddle! Take Coldplay... Huge band, not the most difficult basslines (on the whole) you've ever heard!

BTW, if you haven't got pedals yet, you can still get your LH into shape for when you do... Put the Bass Tone in the RH section of a split (transpose it back down into bass range). Now, have the arranger just play drums, play the bassline with your RH and work on getting the LH doing the comp and chords, etc..

When you go to playing with your feet, the LH now already knows what to do! RH now does melodies, counter melodies, other comping... and voilà! You are an organ player!