Why are Church Hymns sometimes chanted in an abbreviated short tune and sometimes in a long tune?

In the early Church, there were no churches in some villages, and many people would attend their nearest church from sunset on Saturday until the morning or dawn of Sunday to participate in the divine liturgy. The faithful would praise throughout their journey from their village to the church in town, and also after evening Vespers until the beginning of Matins in the morning, so that those present would not be distracted with temporal matters. Longer tunes were clearly useful in these circumstances. But the Church arranges worship according to the circumstances of her people.