There's two major problems here:

1. What republican constituency wants and what republican polices are do not align. For example, most Republicans support Donald Trump. Most do not know anything about Donald Trump's policies. Most will directly say they disagree with a policy, and yet they will still support Trump. If you tell them said policy is a Trump policy, they will either say that it's not true or say that they misspoke, and they do agree with it.

For example, practically all of Project 2025 has been well underway. Prior to the election, it was clear that republican constituents DID NOT support Project 2025. However, if you simply say Project 2025 policies without using the word "Project 2025", then they do support it.

2. Republicans and conservatives at large will just lie if they believe you are willing to make a moral judgment on them.

For example, if you ever go on Hinge or Tinder or whatever dating app you choose, Republican voters will almost all be "apolitical" or "not interested in politics". They will not mention who they voted for and they will purposefully deceive potential partners so they can avoid what they feel is a moral judgement.

Probably republican voters here felt the question was asked in a pointed or morally judgmental way, so I'm sure a good amount just lied and said they do support immigration. If you then poll how many voted for, say, Trump, who is explicitly anti-immigration (not anti-illegal immigration, anti-immigration) then your numbers will change.

Now, this IS NOT to say that republican voters are stupid or liars. The republican party is, right now and for the past decade and then some, run by populist leaders.

This is the direct result of populist messaging. There are also populist leftist leaders - they just do not currently exist in the US.