Nobody is saying toi cut him before his contract ends... You're right. Cutting him would cost us... Just wait til the contract expires and make a decision at that point
The advantage of doing something this year is that you are not under the gun. His contract doesn't end next year, but Dallas does have to make a decision by next year because he's set to make $59,455,000 with no more years left on his deal. By extending him this year, the team has some negotiating power. Players like guarantees concerning future money and right now, Dak has none. His dead cap hit of $61,915,000 is almost all prorated money he has already received. His $29 million base is not guaranteed.
If Dallas believes he is the team's future at QB, then you extend him out now while the cost will be a little lower and you can get him on a longer-term deal to spread out the hit. Dak signed a four-year deal partly because he didn't get an extension that would have included years from his first contract. With two years left on his current contract, it's likely that Dallas could get him on a six-year deal now. So there are advantages.
The disadvantage, of course, is if you want to get out of that contract in the first three or four years, it's going to cost you. But even if you look at the Lamar Jackson $260 million deal, he's being paid $22 million this year and $33 million the next. Even with his large contract, that's better than the $26 million we're paying Dak this year and the $59 million he's due next year. Now, hopefully we would not guarantee him as much as Baltimore did, but there's definite value to redoing the deal now.