There were a handful of potential impact trades made in preceding days, but it was the fewest amount of trades made and total players moved on deadline day since the lockout-shortened 2012-13 season, when 17 trades were made involving 30 players.

Eighteen trades were made Wednesday before the deadline came at 3 p.m. ET. Of the 33 players traded, 17 are playing in the American Hockey League.

The 2017 NHL Trade Deadline passed Wednesday without any blockbusters. Several so-called rental players also stayed with their teams, as did many of the big-name players who had been headlining the rumor mill.

Of note, the Colorado Avalanche did not trade forwards Matt Duchene or Gabriel Landeskog, the Pittsburgh Penguins did not trade goalie Marc-Andre Fleury, the Vancouver Canucks didn't trade goalie Ryan Miller, and the Arizona Coyotes didn't trade forwards Shane Doan or Radim Vrbata.

The question is, why? The answer has four parts, according to NHL general managers.

The upcoming NHL Expansion Draft played a significant role. The potential for minimal to no change in the NHL salary cap for next season was a factor. Parity in the standings made several GMs hesitant. And an unwillingness to move high-end future assets blocked the blockbusters.

"It's just getting more and more difficult to make a trade," Tampa Bay Lightning general manager Steve Yzerman said.

The upcoming expansion draft that will stock the Vegas Golden Knights, and the protection list each team will be required to give to the NHL, were at the forefront of a lot of discussions and the reason many trades that normally would have taken place did not.

The Golden Knights will be required to select one player off of each NHL roster in the expansion draft, which runs from June 18-20. General managers have the option of protecting seven forwards, three defensemen and one goalie, or eight skaters regardless of position and one goalie. GMs were hesitant to add a player they could lose in June.

Video: Vegas Golden Knights GM joins the show

"If you bring in a forward, you have to leave another forward unprotected," Columbus Blue Jackets GM Jarmo Kekalainen said. "Basically you have to include that in the cost of the trade."

Many teams are at or close to the $73 million salary cap this season and have players who need a contract for next season. It led to a minimal amount of discussion and activity around players who have term remaining.

Defenseman Dalton Prout (New Jersey Devils), forward Valtteri Filppula (Philadelphia Flyers) and forward Eric Fehr (Toronto Maple Leafs) were the three players traded Wednesday who are signed through next season.

Duchene and Landeskog, each with term left on his contract, could be traded closer to the 2017 NHL Draft, to be held after the expansion draft, when teams have a better idea of what the salary cap will be and what they lost to Vegas.

The Pittsburgh Penguins didn't want to deplete their goaltending depth by trading Fleury, who has two years on his contract after this season and could get moved after the season and before the expansion draft. The limited market for goalies likely prevented the Canucks from getting a quality return for Miller, who can become an unrestricted free agent.

"It was busy as far as talk, but as far as movement, it wasn't as busy," Dallas Stars GM Jim Nill said. "A lot of that is, you've got a cap that's a flat cap moving forward. It's hard to add bodies."

Video: Big Names Staying Put: Duchene, Landeskog, Vrbata

Asset management also was a reason some key rental players (players on expiring contracts) didn't move. The Coyotes didn't trade Doan or Vrbata, and the Buffalo Sabres couldn't trade defensemen Dmitry Kulikov and Cody Franson or forward Brian Gionta despite trying. Each would have required the acquiring team to lose a prospect or draft picks, or both.

Though some mid-range draft picks were traded in the past week, GMs are loathe to give up a high pick because of the importance of drafting and developing to incorporate young, cheap players into the lineup.

The Washington Capitals and Minnesota Wild, the top two teams in the NHL standings, were the only teams to trade their first-round pick in deals involving rental players during this trading season. The Capitals got defenseman Kevin Shattenkirk in their package. The Wild got center Martin Hanzal in theirs. Each trade was made before Wednesday.

"Teams are starting to hang onto their futures," Detroit Red Wings GM Ken Holland said.

Many teams kept what they have because they think they are in the Stanley Cup Playoff race.

The Toronto Maple Leafs hold the second wild card into the playoffs from the Eastern Conference, but the New York Islanders and Florida Panthers are one point behind and the Flyers are four points back.