If you don't know that yes, this is exactly why people do it, I'd quit asking disbelieving questions until you learn why handloading is so popular.

1) Factory loads in popular calibers are loaded weak because the manufacturer has to account for the fact that they may be used in an old gun design that cannot handle pressure levels of a modern bolt gun. For example 30-06 loads that won't blow up a M1 Garand's gas action.

2) Factory loads have to be set to a conservative length that will chamber in all guns. A handloader can seat the bullet out near the lands, optimizing accuracy and maximizing powder volume (and increasing velocity).

3) Factory loads will always be loaded soft because different guns show pressure signs at different velocities, so they must be conservative to avoid making the shells dangerous in some guns.

So with my 300WM, I can seat 200gr bullets within a few hundredths of the lands and still fit them in the mag, increasing my powder volume. However the shells are past SAAMI specs so they would not chamber in many rifles but that's ok, I care about the performance of only one gun and my shells are only loaded to use in one gun. If I cared to give up a bit of accuracy I could easily load them comfortably north of 3000 fps, with 200gr bullets. The only reason I do not is I achieve maximum accuracy just shy of that.

There is no way on earth that a 300WSM, with a 200gr bullet set to chamber and fit the magazine of most rifles, is going to match this performance.

The difference between good handloaded ammo and factory ammo in the 30-06 is even more striking because factory 30-06 ammo has to be manufactured fearing it will be used in many old military rifles.

Until a few years ago handloading's major draw had a lot less to do with cost savings and a lot more to do with maximizing performance. This is why you see scarce serious shooters out there with factory ammo.

Your "apples to apples" is like comparing a half-rotted apple picked off the ground (your 300WM examples) to one purposely picked at its prime and waxed up to sell better (WSM). Not all apples are the same.