Because -XX:-DisableExplictGC enables Systsem.gc() to work. You need to use -XX:+DisableExplicitGC to turn off calls to System.gc().
If you read the column heading for the options table on the JVM option web page at http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html, you will see that is says "Option and Default Value". Thus by default DisaableExplicitGC is off, you need to use the plus sign to turn it on.
Thanks again Peter for your kind help.
I invistigated about the -XX:UseParallelOldGC and found that it automatically enables the UseParallelGc. Furthermore, It includes a compaction phase to reduce the heap fragmentation and also perform major collections in parallel. Thanks in advance for claryfing to me why you want me to drop it as you can see it appears usufel.