Let's say Seguin, if he isn't traded, has the same development here as he has in Dallas. If we signed him to a 2 year, ~3.5m deal, it would just have ended. He has been well over PPG for the last 2 years, among the league's leading scorers each year (at 23) and I guarantee you he would be asking for 8-9m per season. Look at Tarasenko. He's Seguin, but slightly worse. Just locked up 7.5m after his ELC. But watch closely how he does the next 2 years... If STL gave him a 2 year bridge worth ~3.5m, he'd probably be asking for Kane/Toews money after that.
Bridge deals are a glass cannon... They're very safe and you're guaranteed a steal of a contract for a year or two. If the player doesn't develop as you want them to, that's fine, it's a "prove it" contract. But when you give bridge deals to extremely talented young players like Subban, Seguin, or Galchenyuk, who could break out any season now, it's not worth the risk. That's why Montreal is paying 9m for Subban, and why the Isles are paying 5.5m for Tavares, and Dallas is paying 5.75 for 4 more years for Seguin.
Bridge deals are for players like Spooner and Connolly... To prove that they're worth the investment to have them on the NHL club full time. I would have preferred signing Hamilton for 5-8 years at 6m per year to ~3.5m for 2 years.