The current number of known attacks is not a clear indicator of total vulnerabilities. After all, three years ago there were zero confirmed exploits targeting speculative execution. Intel's architectures have proven more vulnerable, thus far, but to assume something is secure until it's not is totally backwards. At best we can assume that attack variants that a prerequisite on vectors that are categorically absent cannot work, but that doesn't mean other vulnerabilities will not be discovered.
Market share does matter. The more popular something is, the more people are looking at it and the faster flaws will be discovered. 'They', being the sum total of those capable of stumbling upon a vulnerability, is a figure directly related to the number of parts in use and they are, perforce, profiling what is used at the rate it is used. Right now everyone is still running down the low hanging fruit of vulnerabilities related to the same branches of TLB related side-channel vulnerabilities that Intel architectures have proven to be particularly vulnerable to.
...rightful liberty is unobstructed action according to our will within limits drawn around us by the equal rights of others. I do not add 'within the limits of the law,' because law is often but the tyrant's will, and always so when it violates the right of an individual. -- Thomas Jefferson