There are a few issues with there being... a single ideal privacy option line of devices (the Pixels):
- the pixel isn't available for sale in all regions
- there are only so much Pixels out there.. Meaning less options to choose from and potentially higher prices
- people using them stand out... So much so some agencies treat Pixel users like criminals even if they don't have Graphene on it
- Google may choose to end the Pixel line, drastically limit production or remove some feature Graphene relies upon any time they feel like
Having more vendor choice drastically lowers these negatives. And I can't really think of any negatives for the other side than increased dev time and operating costs.
Having the privacy features trickle down to other devices is great since some already landed in AOSP.
However, the trickle down is slow (and often a myth). And some protection is better than no protection.
Why are a multitude of poor options better than a few good options?
Is anything other than a Pixel a poor option?
They may be suboptimal but... Some hardening is definitely better than no hardening any day of the week.
What actively blocking "okay" or even "good" options when "the perfect" one exists should be plainly obvious.
Privacy-consciousness will never spread. Which also has negative effects on the privacy-conscious. Namely point 3 of my little list.