Yes, but somebody still has to pay or donate their time and the 'human' computational time require is pretty heavy for an object detection task.

It's also usually ideal to just have one person label one image, people often miss things or mislabel things. If you want low noise data, you need to have people repeatedly labeling the same image until they reach a consensus. The more objects the more opportunity for confusion, requiring more labeling.

You have probably been prompted to use captcha-like thing for selecting portions of an image containing a street sign. That's object detection, for a single class of object.

To answer your question, yes it should be crowdsourced, yes it is being crowdsourced, but the companies that are doing it are keeping the data to themselves because of the value/expense in collecting it.