A lot of VCs like to take the 'long view' and ensure that the problem you solve is big enough to make your business and their investment grow. If not, it may just not be worth their time and investment.
Sometimes your business numbers don't give good backing to your expectations. VCs don't like that. Either give them proof that your business works or lower your expectations.
VCs usually come into play during the growth stage of a startup. If you don't even have a problem-solution or a product-market fit, you are also not ready for VC funding.
Some VCs just aren't comfortable with the idea of investing in a company operating in an industry they are not familiar with or if they feel they're not adding any value to it.
VCs look for "the X factor" in a startup team and like to ensure that your team is full of the required skills to fulfil the promise you're making in your pitch deck.