EZY do offer holidays, though essentially they are Flight+Hotel. The snag though with Easyjet holidays is that you might see an attractive price, but you might not realise that you have to pay this upfront.
EZY do sell packages, and you can pay deposits on their holidays.
The problem with that is, the agent will add their commission onto the total price, often around £300, and all of that is their profit to keep. To book directly with Jet2holidays online, you cut out the middle man, abolish the £300+ commission
How much commission the agency gets depends on which tour operators holiday, the price of that holiday, and which agency they are. It would have to be a fairish booking to get £300+, and the agent doesn't add the commission on top of what they book. The tour operators pay them their % commission.