Personally I see several reasons why robots are not as extensively used (all of them argueable, of course):
- lack of trust: while you can trust or not a person, if you do it's difficult for him/her to be influemcied to make something like a terrorist attack, while a robot is quire easier to reprogram (if you gain access to it).
- cultural bias: the main example about this would be SSMM (it's quite paradoxal that the Solomai were the first humans to extensivelly use the robots in Interstellar Wars, but are the ones that trust them less in 3I)
- unable to do some things: while a robot can be programd to do many things, until true artificial intelligence is achieved (TL 16-18, depending on the version), they are unable to react to unexpected events, while a human (or other sophont) being is.
- need for maintenance: it's more difficult for a robot than for a sophont to take care of himself. Living things have some self-repair capability, while robots don't.
EDIT:- a sohpont can be made responsible (and so liable) of its acts, while a robot, accoriding to Shudusham Concords, are not, and the responsability goes to its owner. That alone might make robots unattractive for companies that can have accidents (and that's most companies). (END EDIT)
And sure there are more.
As a referee, my players had robots in two occasions, and in both cases they were to give them access to some skill they lacked as a group: one was an autodoc, as they had no medic among the group and the other was an engineering robot, as they had only one player with engineering and their ship required two engineers.