(As every test match is loss making affair unless one of BIG-3 team is playing) but the relegation system came up in existence because of a lopsided fixture in the form of bilateral. Call it the chicken-egg problem.
By the way, how the matches between BIG 3 and other team is a money making affair ? I think it is only the matches between BIG 3 that may only generate expected revenue.
For example; Windies target 2 test series against India and England in a 3-year cycle and it keeps them afloat. The rest of their series hardly mint any money because broadcasters are not into it. The same goes for South Africa. Another example would be Pakistan, which would give you a hint. There was no broadcasting deal for the England tour of Pakistan (3 tests match series), The reason; PCB was asking for too much money and there is no 3-4 year contract but a series agreement and the price tag depends on the bargaining.
No one is interested in Bangladesh media rights, hell even for the white ball series (Australia toured them but Aussie broadcaster didn't buy the rights and it was not telecasted in Australia), forget about the test series. Likes of NZ and SL hardly break even on the investment.