Not sure what you mean by "primary driver", but I was finding even Sonnet quite useful for coding tasks, even about 12-14 months ago (I was too cheap to pay more than $20/month back then, and Opus hit my limits too quickly).

Certainly I get a ton more value out of Opus today, but I could absolutely see someone deciding to limit themselves to 8-to-12-months-ago Opus performance for privacy (or other) reasons.