Question
Why praying is not a compulsion in Hinduism?
Answer
You used an Important word called Force (I will not talk about the scientific force here)
Force ( Meaning ) :
1. Coercion or compulsion, especially with the use or threat of violence.
2. Make (someone) do something against their will.
What is Will : The thing that one desires(and the desire is limited to natural cause, e.g. You had a full meal, but you want to have more, its greed not will).
Hinduism teaches to move in parallel to nature, this is only thing which Hinduism calls to human, and the first principle of walking parallel to nature is doing with your will.
Hinduism believes in Karma, you have your will, do whatever you want, but be prepare for the consequences. Doesn't it looks logical and more natural, a lion never eats with full stomach, neither any animal. Its nature, we are nature, if we force someone against the will, we are actually forcing the nature.
The only thing we can do is teach them the difference between right and wrong, its always a person's choice to choose one.
Now about Pray : What is Pray ? Is pray limited to group of words, which you draft in-front of god. No in Hinduism it has a broader concept, if your Praying just the sake of Drafting words its useless, you need to do with your will, you should have an utter belief in him, you should be ready and gone from other thoughts while you are praying him.
If you pray with your will you are actually thoughtless and your pure intentions are inclined towards him, making it more effective.
Are their rules for Praying(I shouldn't use the word here as its with limited sence) : Their are rules, like Surya Namashkar, which will be helpful in Brahmamuhurata only. But they are not forced to us, why ? again its your will if you want to gain the benefits or not.
What GOD wants : Is he a dictator? no he is a creator, to understand this, just think you created something, you will love to be it what you created. Therefore GOD doesn't wants you to Pray him, if you do he will Please, but If you don't it will not hurt him, he only wants you to take care of the fellow creation.
My answers may feel empty without scriptural proofs, I will try to add some, but this is the overview of Hinduism.
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