4. Cost effective
If the Steelers truly are going to make a change at quarterback, then their other option would be to trade up in the 2024 NFL Draft and select either Caleb Williams or Drake Maye. At least, those two guys are as close to a sure thing as you can get in this draft class.
But, the cost of moving up to the first or second overall pick is likely going to cost a first round swap, plus an additional first, and a combination of 2-4 additional picks with at least two being in the second round.
That's quite a bit for someone who is completely unproven. On the other hand, they could make a trade for Fields who still has one year left on his rookie contract, plus the fifth-year option in 2025. Fields hasn't exactly done enough to merit a bulky extension just yet, and the Steelers would still have two years at a decent price before they'd have to pay him top-tier money.
This way, the Steelers trade less to acquire Fields and keep some draft capital to use at other positions of need. Plus, they get someone who is somewhat proven rather than a rookie who very well might not add up to their draft pedigree (hello, Bryce Young?).