Can you show screenshots showing all 14 deliveries in each case? Otherwise, it looks more like you were "cherrypicking" low offers on purpose: $7, $6.50 vs. "accept all" $8.75, $9.75.

Also, what day of week each day is, and when? Earnings can be very inconsistent from day to day and week to week even if you don't change your method. Just because you found 2 days with the same # of deliveries and same hours, statistically does not represent a reliable data point from which conclusions can be made.

Slow day? Lower your minimum a bit, like by $1. It should still not be anywhere near lowball offers.

Miniscule car maintenance?! You're running your car to the ground, literally. Maybe you just started recently and don't notice it yet. Big repairs are only a matter of time.