There are a few things that you could do to improve your hub:
1. there are some grammatical errors. For example your title is grammatically incorrect. A more correct way of writing it would be "Why Bangalore is known as the Nerve Center of Real Estate Investment." But even that is incorrect - see #2
2. you are using some expressions which come across as stilted and and as non standard English. This affects the readability of your hub. This is a difficult thing to pin down, and I am aware that there are dialectical differences of English as spoken in the Indian subcontinent versus the United States. So the way you have written it is not necessarily wrong, just that it sounds off to someone who is a native speaker of North American English. Since hubpages is an American site, I assume that part of the quality assessment involves evaluating the writing from through a American English lens.
3. You use some acronyms and terms that are unfamiliar without explaining them. For example: MNCs, flyovers and overbridges. I can guess what these are, but they are not common terms in North America.
4. Your hub is clearly promotional. There is only one link, and it is to "buying best flat in bangalore." This link does not add to the value of reading your hub and is meant only to drive traffic to the site you are promoting. This can destroy your hub's quality. Plus, even this key sentence is grammatically incorrect. You say: "Buying best flat in Bangalore is no longer difficult. " This is an overly forced way for you to include the key word anchor text you want. I realize you are trying to improve the SEO of the site and hope that it will show up when people search "best flat in bangalore" but the sentence is painful to read. You need to be more subtle.
4. Your hub tries too hard to convince the reader that these are good investments. As such it is clearly promotional without adding much value, which will hurt your hub's Quality Assessment.
You need to understand that Hubpages wants and needs to eliminate hubs like these because if too many promotional hubs like yours get on the site, they will hurt hubpages rankings in the Google search results. In other words, it is going to be hard for you to get something like this approved because their quality control system is designed precisely to weed out this sort of hub.
If you want to pass quality assessment, read the guidelines carefully and look at some featured hubs to get a feel for what is acceptable. You can have a link to your site, but it should be one of many - with the other links pointing to useful sources of information, not sales pitches.
More importantly, the hub should provide valuable information about Bangalore. Talk about its attractions, its culture. Make the reader interested in this place. Add beautiful pictures and videos.
I hope this helps.
