1. The contemporary performer will for the most part be joined by enhanced instruments. Indeed, even a professionally prepared voice with great projection will require a mic for this situation.

2. The way that contemporary artists utilize certain vocal hues/tones/timbres for elaborate reasons some of the time additionally implies that these sounds don't extend without enhancement.

Western composers over the ages have written a great deal of vocal music which is not opera, that is, which is something other than a stage drama with sets and costumes and acts and scenes all set to music. While many classical singers perform opera, many others do not take to the opera stage at all. There is a lot music for classical singers to choose from, as composers have written sacred and secular choral music, songs for soloists accompanied by a piano, chamber ensemble, or orchestra, and other types of non-dramatic or semi-dramatic music. All of these require 'classical singing.'
The contemporary musician will mostly be accompanied by amplified instruments. Even a professionally trained voice with good projection will need a mic in this case.
2. The fact that contemporary singers use certain vocal colours/tones/timbres for stylistic reasons sometimes also means that these sounds do not project without amplification. Think of a very quiet, breathy, whispering sound in a ballad.