Your photos are of decent quality, but I get the feeling you are not really understanding what a place like Shutterstock is seeking and their reason for existence. You are not alone, many people are in the same boat.
Shutterstock, and other stock photo sites, are NOT art galleries. They do not care, want, or need, "pretty" pictures of landscapes or the side of a building, or trees, etc. They are in business to SELL photos that other businesses use for typically advertising. Look at practically any online ad or at photos you see just walking around in a store. Very generic looking people acting like they are about to have an orgasm looking at a piece of food or holding a phone. The good looking women or men you see smiling and talking on a headset who are supposed to represent who you talk with when you call some customer service number is a shining example of the kind of photos a stock site wants. They are phony as hell, but they are photos created to try to SELL something or convey a message.
Stock sites don't need vacation photos or photos of items that are common and have no real commercial value. Many, many years ago you had a slightly better chance at getting such photos accepted, but now, stock sites already have so many of these photos that there is just nothing for which they have a need.
High quality is not at all the only critiera that stock sites are seeking. It has to be photos they feel will SELL for commercial use. Your photos are not at all in the category. Stock sites are not there to purchase pretty photos for the fun of it or to try to be an online art gallery. It is a BUSINESS and it requires a very certain type of photo.