
Originally Posted by
ER
Why is it less an unsporting behaviour if the incident occurred in the last round and the offending party wasn't expelled from the event during it?
It is indeed no less unsporting, but in previous rounds, the arbiter may have another reason to expel the offending party, from the FIDE Laws:
Article 12: The role of the Arbiter (see Preface)
12.1 The arbiter shall see that the Laws of Chess are observed.
12.2 The arbiter shall:
12.2.1 ensure fair play,
12.2.2 act in the best interest of the competition,
12.2.3 ensure that a good playing environment is maintained,
It is in the best interest of the competition and for a good playing environment that unsporting stalling is called to a halt on pain of expulsion.