What is Paul Ryan's motivation?
Exactly the same thing that motivates EVERYONE in congress in both parties: MONEY and POWER and the prestige and swagger that comes with it. The two parties fight over ideologies they personally care nothing about. They give speeches, make promises, and occasionally pass laws for the sole purpose of getting re-elected and keeping their jobs. Jobs that let them sell votes to the highest bidder and become rich. They can't accept money directly so they trade votes for no-show board appointments or speaking engagements or other money laundering schemes.
But none of our representatives are in DC because they believe in some cause or because they want to make something better. They like things exactly the way they are. Occasionally someone makes it to congress who has good intentions but they won't get committee appointments, won't be allowed to become a sponsor on any bills, won't see their bills make it through committee, and are probably banned from the free haircuts and bowling alley.
So, why is Paul Ryan making sure the Republican party is going to be a failure under Trump's leadership? Because Trump campaigned on draining the swamp and all the swamp dwellers are joining forces against their common enemy. Ryan is willing to loose a few seats in the next election as long as they can blame the abysmal failure during Trump's first term on Trump. The goal is to get rid of Trump.
In reality, losing Republic seats makes no difference to any of the Republicans. The two parties are nothing more than two crooked labor unions joining forces to protect their worker's illegal activities. Where one union loses a worker or two, the other union gains one. As long as everyone gets to keep selling votes, that's all that really matters.
Don't be surprised that Paul Ryan isn't representing you. He doesn't care a bit about what's best for you.