"easily deployable" is part of the equation, but even assuming a clojure app was 'easily deployable', the architecture of JVM apps runs against the interests of shared hosting providers - anyone looking to get more functionality from less hardware.
Keeping JVM engines going, and keeping a lot of compiled apps in RAM, on the offchance that someone makes a request, means fewer apps/sites can coexist on the same hardware. My $5/month PHP plan (hypothetical - I don't have one) - only compiles/executes the PHP when the request is made. If no one requests my site for 3 days, it's all just sitting there, not using any resources.
Until there's another technology that follows a similar model (or something else which provides good economies of scale for hosting providers), PHP will continue to dominate large segments of certain problem spaces.
Keeping JVM engines going, and keeping a lot of compiled apps in RAM, on the offchance that someone makes a request, means fewer apps/sites can coexist on the same hardware. My $5/month PHP plan (hypothetical - I don't have one) - only compiles/executes the PHP when the request is made. If no one requests my site for 3 days, it's all just sitting there, not using any resources.
Until there's another technology that follows a similar model (or something else which provides good economies of scale for hosting providers), PHP will continue to dominate large segments of certain problem spaces.