The book of a Revelation has a pattern where the author would hear something " old testament imagery " and the would hear something completely different. Example- Hear The mighty Lion, see the bloody lamb. It is all based on the idea that Jesus defeated his enemies by dying for them. not fighting them.
The 144,000 is a reference to a military census from the book of Numbers.
He heard the calling of the 144,000, he saw the great crowd that no one could number.
The 144,000 is a symbol of the church, the redempted body of Christ.
The new covenant is not a limited arrangement.
More important is I could be wrong and I also don't care either. Eschatology is the playground of the cults and false religions anyway.