Why there are 24 Tirthankaras only?

The answer to this question can be perhaps available from the 87th stanza of “Yashstilakchulikc” scripture written by Acharya Somdev Suri. He observes:

‘There are indefinite number of Grahas (Planets) – Nakshatras – Stars (Heavenly elements in the sky). But their numbers are shown to be limited by the rule of nature. In the present era of Utsarpini time-span, there are 24 times only when these heavenly elements are positioned in the best location. This is a certainty. Therefore there are only 24 Tirthankaras only not a one less not a one more.

Introduction of 24 Tirthankaras

Sr.No. Name of Tirthankars Introduction
1. Lord Rishabhdev He had a sign of an ox on his thigh. The mother Marudeva had seen 14 dreams, of which the first was that of an ox. He started the religion after a time span of 18 koda Kodi Sagaropam (Sagaropam itself is almost an innumerable number, therefore 18 KodaKodi sagaropam is a countless number) Therefore, he was known as Adinath also (The first one)
2. Lord Ajitnath When mother Vijaya Rani and Father Jitshatru were playing chess; the queen was winning and winning. She did not lose. Likewise, the Lord did not lose. He won the enemies like love and hates.
3. Lord Sambhavnath On his birth, there was plenty of crops everywhere. There was no famine, or draught. All these characteristics were of a good person. Therefore he was known as Sambhavnath.
4. Lord Abhinandan Swami When he was conceived in mother’s womb, Lord Indra made frequent visits and praised Him. People in the family and the state became happy and they congratulated each other. So his name was decided
5. Lord Sumatinat Once mother, while finding solution to a very difficult problem, got good intellect and she could resolve the conflict peacefully. so he was good ‘Mati’. He was known as Sumatinat.
6. Lord Padmaprabh The mother desired to sleep on lotus leaf. The lord also was as unattached as Lotus flower
7. Lord Suparshvanath The mother had a disease on both the sides, but when the Lord Supashva was conceived , she was totally cured and became glittering like gold.
8. Lord Chandra Prabha Swami Mother had a desire to drink the nectar from moon. She had a feeling of coolness.
9. Lord Suvidhinath When He was in mother’s womb, he had desire to perform good deeds. He became one performing good deeds.
10. Lord Shitalnath The father had a very strong burning fever, which could be calmed down by a cool touch of his mother. He also cooled down threefold burnings of the world.
11. Lord Shreyanshnath There was a bed, set out by some God. It was worshipped, but could not be taken in use. The mother used in but nothing happened due to the great Lord’s grace, who was in the womb. On the contrary the world became happyier
12. Lord Vasupujya Indra made Frequent showers of diamonds / Wealth. He got the name Vasupujya from the name of His father Vasudev.
13. Lord Vimalnath When He was in mother’s womb, both the body and the mind became pure with his grace. The Lord, destroyed the unclean karmas with purity of this mind.
14. Lord Anantnath The mother had a dream of a garland made from numerous precious giens likewise, with a thread within innumerable knots, the fever and other illness of people disappeared. The Lord performed worship for indefinite period, for three fold jwelves
15. Lord Dharmanath The mother became more prone to religion. The lord himself was by nature prone to religion
16. Lord Shantinath When he was in mother’s womb, all the disease and misdeeds disappeared. There was peace all around.
17. Lord Kunthunath In a dream, a big pillar made from Jewellary was seen. The enemies became as small as ‘Kunthu’ Besides small tiny creatures were taken care of by the Lord.
18. Lord Arnath In the dream was seen the wheel with jewel and the pillar. This resulted in growth of the dynasty.
19. Lord Mallinath The mother had a desire to sleep in a bed decorated with flowers of all the six seasons. This desire was fulfilled by Gods. The lord won the Moha etc.
20. Lord Munisuvrat Swami Mother had a desire to keep best vows; and she kept 12 such vows.
21. Lord Naminath When the mother was moving on the fort, her luster could not be seen and faced by the enemies. They bowed down. The lord also got the love and hatred bowed down to him.
22. Lord Neminath (Lord Aristhnemi) Aristha means black jewel. Mother saw such black jewel saw a shining wheel. The lord is also as good as sharp edge of the Religious wheel to destroy the Karmas.
23. Lord Parshvanath Mother saw a snake passing by a bed of the king without doing any injury (biting) to the king.
24. Lord Mahavir Swami (Lord Vardhman) There was a constant increase in wealth, crops, prosperity, achievements etc., parents grew with more and more fame. The Lord became fearless, firm and brave.

(Source : http://www.jainuniversity.org/Introduction_24_Tirthankaras.aspx )