Hi, and welcome!
If you're applying for some very popular shops (like web/telephone shops, or shops that are easy and fun and well-paying) here's a few things to keep in mind regarding those shops:
First, there is A LOT of demand for some of them. Dozens of shoppers can request each one within hours of the shops being published. Schedulers then review the requests and approve those that are from the most reliable shoppers and that are for the nearest dates (if for example you can request them for any day next week, the first ones to be approved will be those requested for Monday - so make sure to request the soonest dates).
Second - Badges. If you do even one of them, you'll get a badge proving you've had some experience in doing them before, making it more likely the schedulers will give them to you in the future. If you keep doing them, your badge level will increase, and the schedulers will, at a glance, see you've had extensive experience - and be very glad to give them to you again. Of course, new shoppers are not left out, and are whenever possible, given a chance to start off and earn some experience in every type of shop.
You can also try emailing or calling the MSP that posted the shop, and letting their schedulers know that you have requested it and would love the opportunity to do it - it's not guarantied to work, but it's a small extra step you can take if you want to, and that sort of engagement is greatly appreciated by schedulers, and often rewarded. :)
I hope this helps!