Why should they have to? I wholeheartedly agree we need business engagement with the USG to be beneficial to the warfighter. In order for that to happen, it also has to be beneficial to the businesses involved. The only other option is complete nationalization of the MIC, which I oppose on several grounds.
Many military suppliers (including my employer) already do quite a bit of development work at their own financial risk, in order to earn a seat at the table to even reach the RFP part of the process. More often than not, they'll fail to ever sign a contract, and all that work is essentially a sunk cost. Business leaders have to position defensively against that risk in order to keep the lights on and all those expert people employed. As a result, the defense acquisitions part of a business is frequently not the most profitable part. Exhibit A is T-7A with "loss leader" pricing in order to win the contract. Boeing is very publicly losing money on the initial sales of that aircraft, which I am sure they hope to make up with subsequent sales and SEPM support.
Businesses in industry can survive by having a diversified portfolio (eg. commercial sales, FMS & direct foreign sales, etc.), and/or locking in the occasional big win such as F-35, T-7, or JPATS, built on a sea of lost contracts and much smaller wins.
There are a (very) few big winners in this business. Our modern system cannot support more than a few big defense contractors. For the rest of us, the margins are very thin in all but the worst economies. You don't survive without having other irons in the fire.