Spurs finished Saturday's game with nine men after Simons was sent off following a VAR review for a late tackle on Liverpool captain Virgil van Dijk after 30 minutes.
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Substitute Alexander Isak opened the scoring on 56 minutes and suffered an injury in the process before Hugo Ekitike doubled their advantage with a header as he beat Cristian Romero in the air.
Romero was booked for complaining he was fouled and after Richarlison scored to halve the deficit with seven minutes left, the Argentina centre-back was dismissed for appearing to lash out at Ibrahima Konaté.
Simons is now set to miss Tottenham's matches against Crystal Palace, Brentford and Sunderland over the festive period.
Former Brentford boss Frank said: "We get the first red, which I have seen being given before. I've also said before, definitely a few times at Brentford, I've also seen others and I don't like this as a red card.
"I think the game is probably too big to say 'gone' but for me it is not reckless, he has not come with exceptional force. He is chasing Van Dijk. He is trying to put pressure and then he changes direction and then unfortunately his foot is on his Achilles.
"You can say 'ah you need to be smarter, don't do it' and all that but so we are not allowed to have physical contact anymore? So that's the thing.
"The next thing on that, if he gets three games, how can he get three games for something that is not reckless? That is absolutely wrong and we probably can't appeal it."
Frank also questioned the decision not to disallow Liverpool's second goal for what he claimed was a push by Ekitike on Romero.
"We responded excellently to [Simons' red card]," he added. "Then I think the second goal is a mistake from the ref. I think there is clearly two hands on the back. I don't understand how he can do that.
"We've seen that a thousand times out there on the pitch: someone go up, goal kick, two hands on the centre-back, foul but apparently not in the penalty box. That was the biggest mistake in my opinion. And from VAR. We kept going."
Frank went on to defend Romero despite his loss of composure just when Spurs were threatening a late equaliser.
"I can't see if it is right or wrong that he gives the first yellow," said Frank. "The second yellow, I see two big boys competing. Konaté absolutely smashes through Cuti. It is a foul, nothing more. His foot lands on Cuti's head. Not a yellow, not saying that. Cuti makes a reaction. I guess it could be given but it can also be not given.
"Any player needs to control their emotions and be cool-headed, it is not only because you are captain. You are talking about a very passionate player who has been very good for this club in many years."
