[amsat-bb] Question about PL/CTCSS on uplink

I understand why FM satellites need an PL tone on uplink (to keep out land-mobile services, like taxi-cabs, etc), but why is a PL not required for the linear sats utilizing the same frequencies? A linear transponder is certainly capable of receiving/transmitting an FM signal (albeit not successfully demodulating that signal).

This question came up at a satellite presentation I did, and I had never thought about it. ( Moreover, will radios even transmit a PL on SSB/CW transmissions?)

Philip N4HF