Being the middleman has always been a big deal for people, there has been tons of business ideas like for example airbnb that doesn't own a single house (I assume, or at least very few) but rents other peoples houses and make money from that. Unfortunately the biggest problem these type of business ideas have is the simple fact that you need to be wanted and requested and get a lot of attention for others to join you.

For example, in the construction business you need to find places to actually want to deal with you for you to be able to send your business to others and take the difference, if you can't find business and market yourself well enough, that means you are not going to profit. All those middleman places gets big because they are very well known and wanted in their industry.