That's the case in any country where a parliamentary body is split so closely.
When you need every vote to get legislature to pass, because you control 51% of a chamber, backbenchers on the ideological fringe of a party, (DINOs and RINOs) have a lot of power.
When you have a majority with comfortable margins, you can care a lot less about what the Sinemas and Manchins and McCains of a party think.
You're looking at the world with your American blinders on. The rest of the world's elected representatives vote with their party or they leave their party. What you're describing is a fundamentally American phenomenon.