It costs money to generate certificates and run servers. "Free" web/image/whatever hosting companies make money from advertising, but it does not apply to SSL certs. You can't embed ad in certificate. So they don't make money. No money -> no servers -> no service.
SSL certificates service must be reliable. If its not, its fishy and not trustworthy. If you use their service and something happens to their servers, your visitors (including search engines) will experience issues verifying certificate. That might tank your site's traffic and search engine standings.
Its not worth it. Better pay $9/year for Comodo certificate or not use SSL at all.