They really don't. Plus the Pacers have a massive gaping hole at the 5 and none of the top picks in this draft really fill that holeNot if they win the #1 pick. #1 pick usually gets to help his teams win from year one in most cases. Sometimes even the top 3 contribute positively to winning in a strong draft class. And whoever they draft, a rookie contract holds much more value to a team than Walker who's about to add 20+mil to their salary.
The value question for the Pacers is what could they get if the pick landed #1 vs what could they get if it lands #6. Like Kqwin said if they trade the pick they can win some more game post ASB (though I really don't think it would be that much more, they would still have incentive to rest Siakim down the stretch so they can ensure his health for next season). Also the whole contract situation with Walker and what they can afford and what salaries would have to be moved around to make things work financially for the next 2-4 years (would require more research on my part that I can't do currently)
I somehow doubt the Pacers want to do a rebuild, so it makes sense they are looking to trade. They took the Thunder to 7 games with Turner and Walker is certainly an upgrade and they would be able to get more than just Walker in a trade.