Apple does exactly this, they just launder it out to their carrier partners. My wife's carrier was recently offering a free Apple Watch if you pre-ordered a new iPhone before launch.
Similarly, Apple was already selling a laptop (the M1 MacBook Air) at MacBook Neo prices, but only via Walmart (and they were continuing production of the M1 MBA specifically for this deal).
If you buy an iPhone on day 1 from the Apple store you're certainly not getting any gift or discount. With Google you can pre-order and get a $200-300 gift, wait for deals (Black Friday, Christmas, ...) or if you aren't in a rush, wait six months for resellers and carriers to invariably start dumping their stock at half the MSRP. Meanwhile the base iPhone price has decreased by 10-15% maybe.
And I don't see how older MacBook Airs are relevant here. Apple has always sold previous generations of their hardware for years, directly or indirectly, either by actively maintaining production or simply letting resellers deal with old stocks. Google keeping the previous year generation on their product line-up is a very recent development. Not very long ago they would abruptly stop selling the Pixel N before the N+1 were even announced.
I don't have any insight into what deals the carriers have on the backend, but in my region, the price delta between like-for-like BYOD plans and plans with subsidized iPhones are effectively nil.
Either the carriers are getting discounts from Apple, or everyone with BYOD plans are subsidizing phones for people who get them through carriers.
e.g. I'm currently seeing a carrier plan where the total plan + device cost over 24 months is ~$1,600 and you come out of it free and clear with a 512gb iPhone Air that's $1,749 retail. I don't see how that's possible for the carrier to offer if they're not getting discounts from Apple.
My point is that Apple doesn't want to look like they're giving discounts on their store, so they engineer any discounts to go through third parties.
Phone: 1099 (Apple's MSRP). 24-month phone plan, 50/month the first year, then 81/month: 1572. Discount: -300
Now BYOD:
Phone: 1067 at the biggest and most reputable online retailer. Near identical phone plan sold through our discount/virtual brand: 30/month i.e. 720 over 24 months (but you can leave anytime).
So even assuming you buy it on day 1 with zero discount from Apple's MSRP, that 300 gift costs you 852 CHF really.
Now if I look at our most agressive competitor, you get the phone for free if you spend at least 1752 on a 24-month phone plan.
They have a better phone plan at 15/month i.e. 360 over 2 years. BYOD is still way cheaper.
Like I said, for one of my local carriers, I'm seeing a plan that costs $1,600 that includes both two years of service and a $1,749 MSRP phone.
There's no possible way for a BYOD plan to be cheaper after accounting for the phone MSRP, they'd have to pay you $150 for the SIM card and two years of service.