The cheaper option for Apple would be to use smaller camera sensors with worse performance because that would reduce the depth needed for the sensor + lens.

The cameras are getting bigger because a decent segment of the customers want better performing cameras on their phone.

Either the whole phone would have to get thicker and heavier to accommodate, or you end up with a camera bump. And yes, some people would want that brick phone, but Apple seems to think it isn't a large market segment and the money they print from iPhone sales seems to point to them being decent at gauging that market.