I do not enjoy debating theological nuances with people and get quite uncomfortable discussing the finer points of Christianity. I'm not saying I won't, but I work hard to avoid it.
As with all topics, there are some who can handle differences among friends, and some cannot. Some people's faith takes them to point A, and someone else's to point B. We don't all have the same point of understanding in many areas of life, so why should Biblical insight and understanding be any different? Wisdom should dictate not overloading those in another place than we are. I'm certain my husband is careful with the information he gives me and the kids and he always has been. He carries the load he's carrying and is our protector. The comparison isn't exact, but the same general principle applies with our brothers and sisters in the faith. We need to be careful to perceive when we're not doing someone a favor by making them think about something in a way that is going to strain them or cause them to struggle. The Holy Spirit is the One to reveal the truth He wants to reveal in the minds of a believer reading the Word of God or hearing sound preaching. Right there with that statement I'm revealing something about myself, right? I am not equipped to debate and do not want to. If I wanted to, we'd all hope I was equipped to, but in the moment of a discussion where people disagree, I can't even think straight.
That said:
Question: Did ALL of the people, every single one, go out to Jesus to be baptized? When we approach scripture with a preconceived idea that a word always has to mean X because otherwise it doesn't lead to the conclusion we want, we're not giving an honest reading. "All" does NOT mean ALL every time the word is used. We must look at the context and not be afraid of what the Bible says or is teaching. I contend that not every single person went and I do not think the verse implies it. Figures of speech; they exist. It likely means MANY, maybe MOST, but not EVERY SINGLE person living in each country.
Let's look at this one:
John 6:37-39
37 All that the Father gives Me will come to Me, and the one who comes to Me I will certainly not cast out. 38 For I have come down from heaven, not to do My own will, but the will of Him who sent Me. 39 This is the will of Him who sent Me, that of all that He has given Me I lose nothing, but raise it up on the last day.
Question: Does every single person that the Father gives to Jesus go to Him? Yes, this statement gives the limiting factor. The people God gives to Jesus, all of THEM, will COME to Jesus. (side note: All that He GIVES will COME to Jesus. Isn't that interesting? On God's side, He is GIVING them to Jesus but on the side of people, they are COMING.) Does this say the Father gives ALL people to Him? Every single person that the Father GIVES to Jesus WILL come to Jesus. And of ALL that God has given Jesus, NONE will be lost, they will be found in Him (saved) until the end and will be with Him in eternity.
This is a good explanation, better than I can give. I strive to not repeat mantras that tell me what to believe. I think "all means all" falls in to that category. It presupposes the context so that the verse says what someone wants it to say. We are each responsible to read and study and know the Word of God