DP World Tour members like Ian Poulter, Sergio Garcia and Lee Westwood are eligible for the event at Wentworth after their suspensions for playing in the inaugural event of the Saudi-backed breakaway were temporarily stayed on appeal.
American Talor Gooch and Mexico's Abraham Ancer are in the field thanks to being in the world's top 60, but Horschel believes they are being "hypocritical" in chasing ranking points having never shown any interest in the event before.
"Even though Lee Westwood and Ian Poulter have been stalwarts for the European Tour, I don't think those guys really should be here," Horschel said.
"I honestly don't think that the American guys who haven't supported the Tour should be here. Abraham Ancer, Talor Gooch… you've never played this tournament, you've never supported the DP World Tour. Why are you here?
"You are here for one reason only and that's to try to get world ranking points because you don't have it (on LIV Golf).
"It's hypocritical because of what some of these guys have said when they said they wanted to play less golf. It's pretty hypocritical to come over here and play outside LIV when your big thing was to spend more time with family and want to play less golf.
"I wouldn't call Lee Westwood and Ian Poulter hypocrites because they never said they wanted to play less. The guys that have publicly stated they want to play less, those are the hypocrites."
Horschel believes that players were "naive" to believe that they would not be suspended by the PGA Tour for joining LIV and that some failed to adequately weigh up the pros and cons.
"Maybe those guys aren't smart enough to think on their own and maybe their agents gave them bad information," Horschel added.
"I know for a fact that certain agents just gave certain players bad information and some of those players are ticked (off) that they listened to their agents on that.
"Some of these agents led these guys down a bad road. They didn't give them the entire information and they didn't play devil's advocate the way they should have.
"I guarantee if I was in their seat, my agent would have played devil's advocate, or I would have played devil's advocate. We did talk about what if LIV did come to us, what are the pros and cons.
"And we made a list. There was a lot of cons on that LIV Golf side and very few on the PGA Tour and DP World Tour. There's a lot more pros on that side."
The presence of the LIV players in the field has contributed to lower-ranked DP World Tour members missing out, with Rahm's friend Alfredo Garcia-Heredia currently the first reserve.
"There are many players that have been key for European Tour golf and the Ryder Cup that have a lot of collective years on the European Tour," Rahm said. "Them coming, I don't necessarily think it's a bad thing.
"What I don't understand is some players that have never shown any interest in the European Tour, have never shown any interest in playing this event, being given an opportunity just because they can get world ranking points and hopefully make majors next year.
"A perfect example, a good friend of mine is the first one out on the entry list right now. It doesn't hurt me but it does bug me that somebody who has played over 20 DP World events this year cannot be given the opportunity to play a flagship event because some people that earned it, to an extent, are being given an opportunity when they couldn't care any less about the event.
"They don't know. They don't care. They don't know the history of this event."
Two-time major winner Martin Kaymer withdrew from the tournament last week, telling Golf Digest: "I don't need to go to a place where, feel-wise, you're not that welcome. They don't say it, but (it's there)."
Former Ryder Cup player Oliver Wilson, who won the Made in HimmerLand event on Sunday, did not mince his words when asked about the decision of some LIV players to compete at Wentworth.
"I've got a real issue with the guys that have never played here before coming to play," Wilson told the Sky Sports Golf Podcast. "That's just a bit of a dick move really.
"The European guys that are members, that have played here in the past, I don't really have a problem with that.
"It's an awkward one. This year they haven't had enough events to play in. They need to play other events to keep themselves sharp; Wentworth is an amazing event, I understand why they would come here and play. The fact it's in the courts is sad and it is dividing the players."