Because of how Android works; it's just too restricted for any antivirus app to do something useful. Take a look at antivirus software for Windows. When you install it, it integrates deep in the OS itself, right? During installation, it installs bunch of drivers required for antivirus software to work. It's so powerful it can do anything it wants, heck, even delete system files. Antivirus software on Windows has total freedom to do whatever it wants.
Now look at Android; every antivirus app has just basic permission and cannot integrate deep in the OS. In the other words, antivirus apps have same amount of permission as any other app. Because of this, they are unable to do anything. Can't scan entire Android storage, can't manipulate the apps or do anything without your special permission, can't track app activity to see if the app is actually malicious, can't prevent the app from doing any harm and even if app is really infected, all it can do is say
"please uninstall this app, it's malicious".
Real-time protection is just plain useless. All it does in the background is constantly check apps installed by user which were already "scanned" before installation. It makes no sense to scan already installed apps over and over again, but here we are. The only thing that actually works would be browsing protection, but again, your browser already has one built-in. And you don't need an app for warning you and blocking malicious websites and apps; you can just change the DNS and you get exact the same experience without 2% battery drain.
Have you ever wondered why all antivirus apps on Android are bundled with million other "features" and the protection is like 10% of it? People need a reason to install an app, so how do you make them do it? Easy; convince them they need it (everything in the name of security), just add bunch of features in it, they don't even have to do anything with malware itself, fill it with junk and make user believe it needs that bullsh*t to stay protected when in fact it doesn't. Their job is to make you spend more on features you don't need. They are aware antivirus apps on Android are useless and that's why pretty much why almost all of them are free except few.
Since you have mentioned Kaspersky, I was interested to see what protection "modules" it has. Sure, there's real-time protection which I described above, browsing protection – fair point.
But "secure QR code scanner", "where is my device?", "safe messaging", "password manager", "VPN", "social privacy", "unused app cleanup", "data leak checker", "apps permission manager", "app lock", "identity protection wallet"?! More than half of these Android has built-in! Do you see my point?
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Alright, we covered fake antivirus apps for Android, now let's cover the malware and what it really is.
Can malicious Android app damage Android installation on device? It can't.
Can malicious Android app encrypt all file and data on device? It can't.
Can malicious Android app remove your files in the background without your knowledge? No. Well, unless you explicitly allow it to access your data and to work in the background.
Can malicious Android app install itself or other apps? Nope, not anymore.
Can Android malware be in any other format other than .apk? Nope.
What do you get from this? Android "malware" can't do anything because it doesn't have access to anything. In the past, apps didn't need the permission to do damage. An app could literally manipulate all of your messages, do background calls making your bills high, show you ads throughout Android, access all your photo, video, files without you knowing and bunch of other things. It's 2024 and Android changed drastically. Now malware can't do anything without your explicit permission. Even if you gave it, Google made Android so restricted (in a good sense) that malicious apps can't do more than half of what they could in the past.
And this is exact reason why you don't need an antivirus app. First, you have one already built-in (Google Play Protect). Second, Android "malware" can barely do any damage. Third, antivirus app are everything just not what they claim to be.