My guess what is happening is that: Cloudflare is caching the static assets (js, css, webfonts) and new users download these assets directly from Cloudflare and therefore never hitting your DigitalOcean server.
This means the resource is only requested a few times from your origin server and the rest is handled by Cloudflare; NOT counting to your toal bandwith.
Contrary, in the Netlify case; the asset is also cached on the Netlify CDN however the bandwith is COUNTED against your total bandwith.
You could get the same behavior on Netlify if you would still use Cloudflare additionally:
→ User > Cloudflare > Netlify
In this case, the assets cached on Cloudflare would again not be counted against your total.