Every business is basically a phone number that you can message. It does not matter if you buy a pizza or furniture, book a hotel or need someone to clean your sofa.
No website. No need to fill in forms. No platform fee.
But just because it works that way there, doesn't mean it's right. There's nothing about SEA that implies to me the pinnacle of operational efficiency.
Whilst cheap 'dumb' phones do still exist and are used, even low income earners in South East Asia tend to have a smart phone, and most of the business done as landgenoot says is conducted via Telegram, Facebook, or occasionally WhatsApp or Line.
There are also ways of paying using nothing but a phone number, but usually business is done on a smart phone where photos of products are are shared, delivery is arranged, and since COVID, most payments are done via QR codes that require a smart phone.
In my experience this is not only true of the cities, but also even out in the provinces.