For me it was really the price of domain renewals. Namecheap has great starting deals, but eg. I have a .studio domain and it costs $28.16 to renew at Namecheap and $21.09 at Porkbun. My .xyz domain costs $9.92 to renew at Porkbun, $14.16 at Namecheap. (Registrar comparison chart here.)
In terms of pure price, Cloudflare is cheaper to renew for all the domains I have, but Porkbun is only a dollar or two off and I like supporting a smaller company. Edit: Porkbun offers free SSL which is nice if you don't feel like bothering with LetsEncrypt yourself.
(Also, I find Namecheap's domain management console absolutely horrible to work with in terms of UI.)