There are guidelines with regards to cautionable offences ...
CAUTIONABLE OFFENCES
B1 Unsporting Behaviour
There are different circumstances when a player must be cautioned for unsporting behaviour which include, but are not limited to, when a player:
a) Impedes an opponent with contact
b) Recklessly trips or attempts to trip an opponent
c) Recklessly tackles or challenges an opponent
d) Recklessly kicks or attempts to kick an opponent
e) Denies an opponent an obvious goal scoring opportunity as defined by Law 12
f) Holds or pushes an opponent
g) Commits an offence which interferes with or stops a promising attack outwith the penalty area
h) Excessively celebrates the scoring of a goal as defined by Law 12
i) Handles the ball deliberately
j) Shows a lack of respect for the game
k) Commits an act of simulation
l) Commits any other offence(s) deemed by a match official to be unsporting behaviour
B2 Dissent by Word or Action
B3 Persistently offending against Laws of the Game
B4 Delaying the restart of play
B5 Failing to respect the required distance at restart of play
B6 Entering or re-entering or deliberately leaving the field of play without the referee’s permission
... and if you look long enough, Morelos always "failed" here or there. If the above was applied with equal measure though, how many players would Aberdeen, Kilmarnock and Co. have left on the park when playing us though?
To be found on the SFA's website, on the right under Judicial Panel Protocol (link downloads a PDF.
https://www.scottishfa.co.uk/scottish-fa/football-governance/disciplinary/disciplinary-updates/
BTW, if anyone's got time on his or her hand, the link down on the right "Past JP outcomes" gives you access to pdf-files for all years up to now, so people can check how often teams have been cited et al. Would make an interesting statstic to have.