I appreciate your frankness regarding your situation, it is unusual for a girl's parent to decline the offer especially if you are the same religion and caste, have a good job and earnings.
1.Please think back and check whether there is an issue of a subcaste or heiarchy.Within the same caste there woul various sub-castes and some people are still reserved to give a girl at marriage to a boy from a lower sub caste.
2.Please also check is there any animosity or bad blood between the families, usually if the families have had an unpleasant relationship in the past, then they are reluctant to agree for the marriage.
3.Is there any instance of a love marriage(parents,siblings) or widow re-marriage. Such events although agreed by the world, some families still resent this.
4.Many girl's parents beleive strongly in Astrology and some horscopes do not match ( bride and bridegroom), even if they match, there would issues with finanical loss, illness, death in the bride's famliy and chances being a childless couple. These would be some strong reasons for people to refuse a marriage offer.
5. Also recollect if there is any issues with your character related to you that would have reached the girl's parents.
6. Are there any siblings in the girl's family (elder sister or elder brother) who need to be married first. Is the girl you love working and contributing to their families income signficantly.
Once you know some answers, then give it some time and first you both who are the would be couple sit down and frankly assess the options. Can you both agree that you have the commitment to stand by each other for life, take up responsibilities of the new family. If yes, then would either of you agree to stay apart for few months and give the family some time to change their mind. If they don't would you both be happy for a registered marriage. What are the views of your parents. There should not be an iota of doubts in both your minds and the bond of love between you too.
After this meet up the family with a few common family friend or adults who have the mindset to negotiate an understanding rather than being short tempered people who would make things worse. The ask the girl's parents what is the real issues. Offer them that at least solemnize an engagement and if they want to postpone the wedding for a year or so, let them know that you both would be happy to wait. Give them some time and then meet up once more with a firm view expressed that you both would be going ahead with the wedding with their blessings. Patience and persistence helps in such situations rather than arrogance and hasty decisions that we often see in the movies and TV serials.