Because it won't pass, and you know it. Which illustrates the point that bringing up the border in the context of a Ukraine aid bill isn't about the border at all. It's just a poison pill to kill aid to Ukraine.
Attacking Democrats by saying they're willing to protect other country's borders but not our own is a great argument, and we should jam it down their throats in the context of elections. But whether or not we give aid to Ukraine should pass or fail on its own merits.
Your response proves you know nothing about negotiation. Your style of Republican gives everything and gets nothing. It’s what’s led many to the realization that perhaps the leaders in the GOP WANT to get nothing - because they and the Democrats are on the same side.