I believe the answer lies towards the end of the parable and the last few verses of the chapter.

“There will be weeping and gnashing of teeth when you see Abraham and Isaac and Jacob and all the prophets in the kingdom of God, and you yourselves thrown out. Indeed, some are last who will be first, and some are first who will be last.”

It doesn’t seem to me that some are excluded from entering, at least not eternally—but rather those we think of as first will be last, and those we think of as last will be first. Or perhaps it’s those that believe themselves first, that will be last, and those that believe themselves last, that will be first.

“Jerusalem, Jerusalem, the city that kills the prophets and stones those who are sent to it! How often have I desired to gather your children together as a hen gathers her brood under her wings, and you were not willing! See, your house is left to you.”

In the above verse, we see Jesus giving the meaning of this parable. In their current condition, the Jews are not fit for the narrow gate. They have rejected him. And he has shut the door on them. Not out of disdain or some sort of vengeance, it’s clear that Jesus loves his brothers very much, so much that he weeps for them—but that he rejects their entrance into His life while they believe themselves worthy and ‘first’ to enter. As Spurgeon puts it:

“Men do not like Christ's way of saving them. He does not like it because the "gate of heaven" is not quite high enough for his head, and he does not like stooping. That is the chief reason ye will not come to Christ, because ye cannot get to him with your heads straight up in the air; for Christ makes you stoop when you come."

“And I tell you, you will not see me until the time comes when you say, ‘Blessed is the one who comes in the name of the Lord.’ ””
‭‭Luke‬ ‭13:28, 30, 34-35‬

It would appear, those that have been shut out, may yet have hope.

When we see ourselves as last, the smallest of men, the chief of sinners, the uttermost farthing of mankind; our big heads and our engorged egos are not so big as to not fit through the narrow gate. Then we cry out, not “let us in, let us in”, but rather we cry “blessed is the one who comes in the name of the Lord, have mercy on me a sinner”.  And the gate Himself opens to us; “a broken and contrite heart, O God, you will not despise.”
‭‭Psalms‬ ‭51:17‬ ‭