Vulnerability counts
Jesus what is it with you idiots thinking vulnerability counts mean anything? Linux distributions include a far wider range of software than Windows does, so of course they will have more security issues. Plus there are multiple distributions, so the same issue will be reported multiple times. You would need to include Windows with Windows Server, IIS, SQL Server, Exchange, Office, Outlook, Skype plus a bunch of third party software to equal all the things that ship as part of RHEL.
As for iOS, Apple is the ONLY company that reports every single security issue they fix to get a CVE number assigned - even issues they discover internally. Read Android's release notes next time and note all the security issues that get fixed without a CVE number. All of Apple's security fixes include a CVE number, so their count is artificially much higher.
Even without that, there are plenty of ways to count things. You could discover 12 bugs in a single component, and if they are reported all at once, get a single CVE that covers them all. Or you could file them all separately either deliberately or because they weren't all discovered at the same time, and end up with a lot of CVEs assigned for the same component that has a common fix.