The average car has the manufacturer's logo on the front and back. Usually that's the extent of the branding. It is discreet and under-stated. Sometimes with the higher-end luxury cars you don't even get the model name and engine size given on the boot. A 'less is more' approach seems to work for cars.
Now take a look at a race or rally car. You get stickers everywhere to let you know who supplied the tyres, brakes, headlights, oil, petrol and other parts, e.g. what the hi-fi would be if they had one. Invariably these are sponsors logos, paid to be on the car. Sometimes boy-racer wannabees have similar sticker collections on their cars but they are rare exceptions, most cars keep the branding simple.
The same goes for the interiors, the parts do not have huge supplier names plastered all over them. There are occasional exceptions, 'GTI' models with 'Recaro' seats, forty-year old Porsche cars with 'VDO' dials and that is about the extent of it.
Now take a look at your average bicycle. Why is it a rash of tacky logos? Why does every component with the exception of a few generic parts on low-end bikes have to be disfigured by the make with model? This is particularly tedious with the big brands that get their own parts made for them. Why cannot Trek just have their logo on the frame and keep it clean? Why do they have to litter the entire 'finishing kit' with 'Bontrager' logos? It is not as if the average Trek buyer really needs to be reassured that they have 'Bontrager' stickered handlebars every time they look down to change gear. The after market for 'Bontrager' handlebars isn't exactly huge either.
So why is it that bikes have to be covered with childish logos everywhere?