Palace won 3-0 at Anfield on Wednesday night via goals from Ismaila Sarr, twice, and Yeremy Pino. Amaro Nallo was sent off for Liverpool late on.
Afterwards, Slot said: "It is always a blow to lose a game of football, especially if it leads to going out of a competition. But it is the same selection I did tonight as I did last season in rounds like this. There are many reasons, maybe, why we've lost six out of seven – none of them are good enough to accept losing so many. I can come up with arguments or reasons, but none of them will be enough to go to that standard because at Liverpool losing six out of seven is always too much.
"If I look at our performance against Brentford, to use that as an example, two days after we played Frankfurt away, I saw there a team that maybe struggled with playing three games in seven days. Again, not an excuse to lose that game of football, but it is not a complete surprise to me if I see some of the struggles some players have had in pre-season and players that came from different leagues and it is a new challenge for them to play at Premier League and Champions League level in three games in seven days.
"So, again, in two days we play Villa and the last time I played a player we thought was ready for their programme but it turned out maybe he wasn't was Alexander Isak when he went out with an injury. Last time we played Southampton, Giovanni Leoni went out with an injury in a game like this and we got the red card for Hugo Ekitike after two yellows.
"I think at this moment in time, with only 15 or 16 players available – and I am talking then about players of our squad available – and to add to that this club has always used this competition to use their academy players as well – the non-starters and the academy players – it felt to me as the right decision and I haven't changed my opinion about that after the result because with our starters we haven't been able to win a lot from Palace as well."
On Nallo, Slot added: "I didn't need to say that much. Because another thing which I liked – it's not the most important thing – but Ibou (Konate) and Virgil (van Dijk) immediately went inside to talk to him.
"So that tells me that they are great human beings in a moment like this when a young player for the second time is being sent off – maybe the first time after he played against PSV (Eindhoven), I'm not 100 per cent sure, but I think he did – that they feel how difficult that moment for him is, to go inside and be supportive for him. So it wasn't needed that I took care of him. These two already took care of him."