I’ve made some apps that have had millions of downloads that I launched with no ad spend whatsoever, just good old fashioned viral growth. It got a tonne of copycats but that was OK because I just made the app better in response.
Now, your app is competing against all the inevitable copycats - but those copycats can now just outspend you on ads. They no longer have to make a better product, just have a bigger budget. People are lazy and download the first result a lot of the time.
AppStore search is famously awful enough as it is, ads make it even worse.