While this is likely true, the problem is W2 labor tends to be compensated on a more or less fixed price per unit of time basis, and to cover that cost, you need to bill clients roughly in proportion to total labor time spent, and most clients aren't going to purchase something for an unknown price to be named later. So you need to estimate to give them a price.

From the perspective of the seller, these estimates don't even need to be "accurate" as long as you're making many of them and the errors are symmetrically distributed. There's even math theory behind this called Fermi estimation. The problem is, from the client perspective, they can't average out the errors over many estimates if they're only buying one thing, and from the seller perspective, I don't think our errors are symmetrically distributed. Instead, we consistently underestimate how long something will take.

It's not even unique to software. There's a huge housing boom going on where I live, with condo developments all over the place, and not a single one is actually ready to open by the season their sign out front claims they'll be open. Defense acquisition. Highway construction. Everything takes longer than budget forecasts claim.