Too many Brits in Parliament plainly favor the European Union over their own nation. That’s what opposition MPs seem to do, as they look to block a no-deal departure from the EU by Great Britain, even expressing a willingness to bring down the government to achieve that end.
Prime Minister Boris Johnson wants a (new) deal, for all that he’s willing to take Great Britain out of the EU on schedule if Brussels continues to refuse to negotiate at all, much less in good faith. The MPs’ obstruction serves only to undercut such leverage as Johnson might have in these post-May efforts.
The most that can happen from their obstruction is the preservation of May’s Northern Ireland border agreement that gives open and unfettered entry into Great Britain. This destroys British sovereignty by eliminating its control over its own border—which was a major motivation for the Leave vote.
Since those MPs know this full well—after all, they’re highly intelligent and at the top of their respective parties—their motive can only be their favoring the EU and subordinating their own nation and its sovereignty to that continental entity.