Three reasons.
1) In 2004, the majority of WWE employees had never met Jack Tunney let alone wished to attend his funeral.
2) Those that did know Jack were probably busy since Jack died the weekend of the Royal Rumble that didn't happen. With RAW, Smackdown and the build to WrestleMania starting, it was probably rather busy.
But probably the most important reason why is number three.
3) In the end, Jack Tunney and Vince McMahon did not get along. Which is rather sad because when their business relationship started, Jack was rather loyal to the McMahons.
When Frank Tunney (Jacks uncle) died in 1983, he left his shares to his son Eddie and nephew Jack. They at the time were in a partnership in Toronto with George Scott and Jim Crockett while also in a partnership in Buffalo with the McMahons. Eventually Crockett couldn't spare talent so far north and the Tunney's essentially struck a deal with Vince Jr in joining them in Toronto and thus breaking away from the NWA. That deal was made at Vince Sr's funeral in 1984. It also included George Scott directly working for Titan Sports.
Jack and Eddie didn't get along that well and after a fight, Jack nearly sold his share to Eddie until Eddie actually came up with the money to buy it. But come 1989, Vince struck a better deal with Jack which essentially led Vince to take over their partnership and make Jack President of Titan Sports in Canada. So essentially he really was President.
However this deal really cut Eddie out despite Jack telling Eddie that Vince planned on keeping Eddie around too at Titan. Eddie sued Titan Sports AND Jack. The incident nearly caused Vince to pull WrestleMania 6 from Toronto as late as that spring. Eddie, being sly, even bought the copyright to the name "WrestleMania" in Canada which Vince had to later go back and buy from Eddie. Eddie and Titan Sports settled out of court, but Vince essentially held Jack responsible for the mess.
Fast forward a few years. Former WWF referee Mike Clark was apparently sexually propositioned by Terry Garvin. Jack Tunney was said to have witnessed this in the Toronto office. Jack planned on backing Mike Clark up in court. WWF higher ups didn't like this as they wanted Jack and Mike to just let the incident go for the greater good of the company.
Towards the end, it is said that Jack believed Bret Hart got him sacked. Mainly because Jack didn't think Bret Hart could draw money and thus didn't approve of his main event push. But obviously the rest of the office did think Bret should get the spot. Not like they had much choice anyways. So in 1995, when the WWF was hurting for money, Vince decided he could run shows in Canada without Jack Tunney. He essentially retired him early, made Gorilla Monsoon President, and moved along. Naturally Jack was not happy with what happened and mouthed off at various times over the years regarding it all.
So that's likely why nobody from WWE attended Jack Tunney's funeral. It was mainly bad business that splintered everything.
I know George Scott is still alive, living in Florida. Vince honored him at a house show in 2001 for helping to put WrestleMania 1 together. As for Eddie Tunney, I have no idea if he's alive or dead. But if he's alive, I'm sure he has no love loss for Vince.