How to be truly desireless

How can one be truly desireless. People without desires are usually shown worshipping God. But why would one worship God ? People worship God for various reasons like to obtain his love , Siddhis or just for freedom . But aren't even these things a form of desire ??? Some desireless people are shown helping other people not for selfish reasons but love for mankind /empathy. But if helping others give you joy then your desire is joy.

Also a question not related to title - How do people have so much genuine compassion and love for mankind that they help them without any desires like joy or happiness . Some people who are born with that level of empathy might be doing it but how would people who were into bad practices or just non religious turn so selfless.