I think people are overthinking it with Croft.My theory on Croft - Seibold may have known Croft from his Melbourne days and was putting out the "feelers" for Croft to come to Brisbane. Bellamy caught wind of this, chucked a tantrum and dropped Croft for disloyalty and because he knew he didn't want to be at the club.
It's not like Croft is in isolation, they've had to basically clear the decks going into 2020 with massive turnover of personnel, which suggests they're under cap pressure most likely.
Croft was on an apparent 400k and with a determination to use Smith as a Halfback/Playmaker in an ever growing capacity, a genuine Halfback like Croft could easily be seen as surplus to requirements. Smith is approaching retirement, Bellamy has indicated that this contract may well be his last too, so you have two guys nearing the end of their time at Melbourne and they have obviously, for better or worse, decided that Smith as Halfback is their best chance to secure another Premiership before their time is up.
They've realistically gambled on short term success and only time will tell if that gamble paid off. If they can make it pay with a Premiership, many would agree it was worth the risk and possibly even the fallout afterwards when they both retire. Either way, they most likely won't be dealing with those consequences themselves, so you can see why the gamble was an easier one for them to take.