One huge advantage of paper over computer systems is that it's typically very easy to accidentally delete digital data (and cheap or poorly-architected systems often have no way to restore data), while it's more difficult to accidentally destroy a piece of paper. Moreover, in many digital systems it's possible to delete a record and not even know it, which is less likely with a paper system (and if one knows, then one can often just create a new paper record, no problem).
And of course a piece of paper will still be legible in a decade. Will a digital record?
Paper's not perfect, but it's not bad.
I would really want to know how much business would some car mechanic in pleasantville missouri would see from having a web page.
In particular with car mechanic I would like to know the cost of basic services like tire rotation. I know it's $20-$30 at a major brandname, but I could use a local shop so I don't have to drive out of my way. Some car dealers service departments now have online services to schedule appointments and such, I think half of that can be repurposed for a small car mechanic shop as well.
(This is why I've taken photos of some restaurants in Google Maps and posted them; they aren't doing any advertising on their own so it's nice to help them along and get more visitors).
(on the other hand, given they advertise a lot on podcasts and the like, they may not be targeting traditional local businesses.)
Its a lot to take in, to be sure, but you can't beat the scale of the internet for getting your message out.
They pay suppliers with cash or cheques, they pay employees with cash or cheques, they take orders over the phone or via walk ins.
There are a few companies like Sage Software that do have all in one solutions for self employed to SMB's but again they still require quite a bit of time investment to manage.
It's also important to note that many SMB's at least usually "computerize" (jesus what is this the 80's) at least one thing and that's accounting primarily for tax reasons but most of them don't maintain their own books for this purpose and use an accounting firm so whilst tech is use the 500 SMB's that use a single accounting firm don't need to buy their own accounting software since most firms aimed at SMB's would offer a SAAS accounting platform or some way to upload your spreadsheets.