To make your question even clearer. The shops you see are the ones available to you. But, there may be other shops in your area that are not available to you if they are on a rotation where a certain time period must elapse before they show up and become available.
The reason may be that you have done them the previous month and the time period must be correct before becoming available.
Sometimes the shop was taken by another shopper and was performed when the site was closed. There are shops where another shopper flakes and decides they cannot do the shop, or, they did it so poorly that it must be done again.
Those can be the shops that show up on your list at the end of the month with a very nice bonus.
As for bonuses, you need to do the math to decide if the bonus makes the shop worthwhile. For me, often, its not even the worthiness of the bonus that makes a shop worthwhile. For instance, today, I'm doing some shops that are in an area that is rather fun and enjoyable to be in. I always look forward to them and don't mind the drive (which in itself is easy and scenic).
Each to their own.