Twenty-five years ago, the Big East Conference pulled off two feats not since repeated: It put three teams in the NCAA Tournament’s Final Four, and all were private schools. Unfortunately, both the Big East, and private schools regularly contending for championships, are in danger of extinction. The reason? Football.

The Big East’s greatest year was 1985. Yes, this year the league has several top seeds, and last season it produced three number-one seeds and two Final Four teams. But none of that can compare.

In ’85, St. John’s, Georgetown and Villanova all made the Final Four, and Villanova defeated the Hoyas in perhaps the greatest upset in tourney history.

The conference has remained a hoops powerhouse since then. But it has also been in constant flux thanks to its need to compete in big-time football, by far the biggest moneymaker in college sports.

Founded in 1979, the Big East didn’t sponsor football until 1991. When it did, its overwhelmingly private complexion was drastically altered, with Virginia Tech, West Virginia, Rutgers and Temple, as well as the private University of Miami, joining primarily for football.

Meanwhile, many original members didn’t hit the gridiron at all.

With football conferences of at least 12 members able to stage cash-cow championship games, the relatively small Big East remained vulnerable to poaching. And poached it was: In 2003, the Atlantic Coast Conference grabbed Miami, Virginia Tech and Boston College.

To save its life, the Big East brought in Louisville, South Florida and Cincinnati for football and basketball, and Marquette and DePaul for hoops.

The Big East has survived, but only with eight basketball-only and eight football schools. That balances football and non-football membership, but also makes it impossible to bring in more football schools.

Meanwhile, the gridiron market hasn’t cooled off: In pursuit of conference championship dough, last year the Big Ten announced that it would explore expansion. And the Big East is in its sights. According to an assessment released two weeks ago, Rutgers is a very attractive candidate, as are Pitt and Syracuse.

So why can’t schools like Georgetown and St. John’s play Big East football and end the constant poaching? After all, Notre Dame is private and plays top-level football. Ditto Southern Cal.

A few private institutions do, indeed, play major college football. But of 120 Bowl Division schools only 17 are private. Many of those, such as Duke and Vanderbilt, are perennial doormats.

Most private institutions simply aren’t large enough to compete with the publics. Thanks to massive taxpayer subsidies, public universities are much bigger and cheaper, and can bring in far more students. That leads to many more fans and more potential sports donors.

The problem is reflected brilliantly in game attendance. In 2009, average crowd size for Southeastern Conference games was 76,288. At SEC-member Vanderbilt, it was only 35,015. In the ACC, the average draw was 51,249; at Duke, just 26,314. The Big Ten average was 71,769; but Northwestern a mere 24,190.

The upshot of all this is smaller schools have less money to hire big-name coaching staffs and build Taj Mahal athletic facilities. And private schools need donors to contribute to their whole operation – unlike publics, taxpayers don’t underwrite private schools’ academics – making it less likely that benefactors will focus on sports.

Unfortunately, football’s massive weight is smothering college basketball. In particular, the game is being dominated by “power conferences” – which except for the Big East consist overwhelmingly of public institutions – that not only play Bowl Division football, but are part of the exclusive Bowl Championship Series.

Since 1998, the year the BCS started, only three non-BCS teams have made the Final Four, and pre-Big East membership Marquette was the only private school among them. In contrast, in the 1970s and 80s, such private institutions as Jacksonville University, UPenn, and St. Bonaventure made the promised land.

If the Big 10 nabs Rutgers, Pitt or Syracuse, private-school hoops will sink even lower, with the Big East likely to crumble and ’85 contenders Georgetown, St. John’s and Villanova forced into mid-major status.

Twenty-five years after the greatest postseason ever for a college basketball conference, we could be staring at both the end of that conference, and another nail in the private-school hoops coffin.