If you put the cash in your pocket, how will the business pay it's suppliers, utilities, professional fees, subscriptions, etc - you know, all the things you pay online??
And how will the owner pay his own household bills, again, utilities, mortgage/rent, etc etc.
Presumably, from the non-cash payments - you can minimise the amount of bank funds-processing fees that you have to pay, but not completely eradicate them.
People may work from premises where they also live, so it's not necessarily always plain as to which costs are personal and which business.
As for suppliers, that also depends on the nature of the business. Your suppliers may be big wholesalers, but they may also be local people; e.g. if you run a cafe that sells magnificent cakes that are home-made by a local retired lady - she may well prefer you to pay her in cash rather than a bank transfer. Similarly, you might be an artist whose major value-adding costs are your time and skills, rather than tangible items that you have to pay somebody else to supply.