It's not an unreasonable assumption either. Nick Clegg did seemingly get rewarded for tanking the lib Dems. The ones lower in the party hierarchy will also have seen plenty of examples of pyrrhic loyalty being rewarded.
What modern parties effectively teach - UK Labour is just one of many examples, not even the only example in the UK - is that the supreme political virtue is loyalty to decisions taken in rooms you weren't invited to. That, they think, will eventually get them invited to those rooms.
The sad thing is that whether the rooms actually exist or not, the result is much the same.
"Don't obey in advance" is Tim Snyder's first rule against tyranny. While that is a great moral rule to follow in tyrannies, all organizations want people to obey beforehand, whether tyrannies or not. It's called showing initiative, doing what's needed without having to be told explicitly, and no organisation can function without it.
But in organizations with opaque power structures, where it's expected that decisions are taken unaccountably ("Noen har snakket sammen", loosely, "There has been discussion", used to be an ironic phrase in the Norwegian Labour Party), people may easily slip into obeying in advance a tyrant who doesn't even exist. They're trying to please the responsible people who are surely in charge somewhere nebulously above them in the hierarchy, but those people don't exist, it's bullshitters like Starmer all the way to the top.
Snyder's had his first rule, but I have a first rule too, which I keep repeating, and that is that powerful people believe in all the stupid things regular people believe in. They just act differently on the beliefs. A common person who thinks covid was an ethnically targeted bioweapon rants about it online and gets banned from Reddit. A powerful person who believes it, thinks "it's important that we too get such a weapon, and don't trust experts who say it can't be done, they probably just have scruples". A common person who thinks a Jewish cabal rules the world maybe pesters his relatives with it all day. A powerful person who believes it - well, he's more likely to do something like what Starmer has been doing the last decade. You don't try to fight Bilderberg, obviously, you try to get invited to it. Once you do, (like e.g Jens Stoltenberg was) you probably get disappointed and try to figure out who the real competent ones behind them too are, and how to join them - but you're not terribly disappointed, because on the way up you've been rewarded by all the others who thought they'd be rewarded for supporting someone like you.
Simpler take: The middle ground has been hollowed out. The old method (appeal to the centre) does not appear to be working. Starmer's throwing stunt policies at the wall to try to get some purchase.
It certainly is. And he'd maybe use more classy words for it, if he ever could be convinced to talk about his sincere beliefs. But as I said, I'm fully convinced that powerful people believe all the out there things that regular people believe. We've seen so many examples of it over the decades, and it's otherwise very hard to explain why Starmer would keep doing things which are neither a popular thing to do or the right thing to do.
The simpler take you propose doesn't work for me, because "throwing things at the wall" suggest unpredictability to me, and Starmer has been very predictable if you assume what I have been assuming for a few years now. His actions are not the actions of someone who would try anything, quite the opposite.
When the action is clearly going to hurt their political career, and there's no indication that it will put money in their pockets, and they don't even make much of an attempt to claim they're fighting for a principle, yet they clearly have a purpose in mind and keep doubling-down on it, you have to start looking for a motive somewhere else. "They hate their own people" comes to mind, but that's not really an answer because it still leaves you looking for the reason why they hate their own people. Not all leaders do, after all.