You can, if ISP provides business accounts, and if you're a business customer of your ISP. If you're a business customer, you'll be able to have a secure site, and you can conduct business on your site, and will be able to have your own domain name.

Large ISPs generally offer business and corporate accounts, smaller ISPs don’t.

Because you get better service and a better deal from a specialist company. The hosting services from the companies we use have high speed connections, are secure and offer 24x7 expert technical advice.