Well, we are unfortunately seeing more of this with the rise of populism. However, I feel as if certain factors come together to provide a pretty effective stop-gap:
1. Members of Parliament (MPs) represent roughly 70k people. And while that's still a significant number, it's small enough for them to know and be known by their constituents. It's more difficult to vote against your constituents when you know them.
2. The House of Lords (HoL) can revise and delay, but not block, which means we are functionally immune from cross-chamber games of chicken that result in US-style government shutdowns, or European-style budget bills as confidence motions. We did come pretty close to this with Brexit in 2019, but this was all within the House of Commons given that the ruling party did not command a majority.
3. Parliamentarians usually respect the inertia of institution. As in, the idea that it's right to continue things as they've always been done, unless there's a compelling reason. It's why we're still a Monarchy, why there's still bishops and hereditaries in the House of Lords, etc. Basically, there's a culture of incrementalism. Because if you don't have the inertia, you appear to lack legitimacy, it's just a gimmick.
4. And on the heels of that, I think Parliamentarians have an occupational understanding of the adage "With great power comes great responsibility."
5. The Civil Service, while ostensibly neutral, tends to resign when asked to do anything believed to be damaging to the country.
All of this put together (and probably more than I haven't thought of) means that MPs understand that they could do great damage, and so they restrain themselves.
Contrast this with other countries with difficult systems where politicians stir up the passions of their constituents by naming their systemic limitations, "I would love to do X, but I can't because Y prevents me." A somewhat related example would be abortion in the US, where after Roe v Wade was decided, many states became soapboxes for anti-abortion rhetoric. It's a safe rhetorical position: you can say what you like and then blame the federal government for not being able to do it. But then Roe v Wade was overturned and many of these politicians and states have changed their tune, because the power is now in their hands, they are now answerable to their constituents on this matter. Not that it matters given how much gerrymandering there is, but still, the effect was noticeable.