Anything can be done
The "why not" is generally "something else is a better choice" for subsonic hunting loads, broken down into two general trains of though - bullet choice and case volume.
Bullet choice is rapidly turning into a non-issue in most instances. The things here are will they expand and will they stabilize. You already found Makers, they make subsonic-specific bullets designed to expand in the velocity range. I use Makers in 308 cal and they're great. We're fortunate to be getting a lot of options from a lot of manufacturers now. But the selection is limited in certain calibers because the bore is only so wide, so a bullet can only be so long and stabilize in a reasonable twist, so the bullet can only end up so heavy, which works against keeping it slow. Next is stability - the 175s you mentioned require an 8 twist to stabilize. Not an issue in anything setup for the long bullet trend going on currently (and you're building so you get to pick), but can be a problem for older rifles with slower twists. If you had an old 270 with a 10 twist then that might not work because they barrel can't stabilize the bullet, and that's a hard stop until the barrel is changed. At the point you're putting on a new barrel, maybe look for something more subsonic specific with a larger bullet selection.
Case volume is a problem because you don't need much of it to start with, and the powders that work best with subs tend to be shotgun and pistol powders that would result in low fill ratios in large cases. TB and Tin Star are two good choices for packing large cases to a better load density, but there isn't a lot of options if those don't work for you. My TB experience in 30-06 (same parent case as yours) was that I still didn't need a lot of powder to get subsonic even with heavy bullets (with the smaller bore you're double stacked against here). H4895 is a good option for reduced loads, but for large case subsonic rounds it would take a very reduced load. I didn't find a 30-06 sub load with H4895 before I gave up on it. If you end up struggling to get slow enough even using TB you'd need to look to a smaller case (ie 6.8 SPC) to shoot the same bullets with a much smaller case volume to increase powder options. At the point you're looking for a new chambering, maybe look for something more subsonic specific with a larger range of powder options.
See how those two got to the same point? That's the general why not - if what you're doing is marginal then there are better options out there. A larger caliber will have better bullet options because you want heavier, not lighter, and a larger bore is an easy way to get heavier bullets. A smaller case will increase the number of powders you can use because a lot of case volume just isn't needed to hit subsonic speeds, even with heavy bullets.
Now the "why" side. You can make a subsonic in pretty much anything if you work hard enough, and there are good options specifically in 270 Win to accomplish that. If you want to keep options open for full power loads, maybe these why-nots for subsonics don't outweigh the benefits on the high power side, and the trade offs here are worth it because there's a second goal you're trying to meet other than subsonic use.
