Apostles means one who was sent. Several people were called apostates. But not everyone.
The 60 that the apostles sent a called disciples. As all followers of Jesus Christ are disciples and Saints.
The only differentiating factor is the 12+ Paul and those who journeyed with the apostles were called apostates.
So they had a very unique position in church history.
As the 13 apostles died, there is absolutely no mention of anyone else being called an apostle.
The answer is simple, that unique included special authority and Holy Spirit given powers other than the nine gifts of the Holy Spirit.
So the role of apostles ceased. But the role of disciple continues to this day.