There are two answers to this question.
The first is that any question of the form "Why do (or do not) all members of some group of people do a certain thing?" must be answered by pointing out that people are not uniform, that there is a wide range of variation in belief and practice in just about any group, and that one would have to know what is in the minds of all members of a group in order to answer a question about their thoughts.
The second is that it is hard to know what you mean by "believing in" ashrams. Here is a definition of an ashram from a kriya yoga site (link below): "The word Ashram describes a house where a true Guru is living and teaching God-seekers seeking spiritual advice and help." Probably you don't mean "Why do some Hindus not believe that ashrams exist?" (which is what we usually mean by "believe in"). If you mean that they do not all follow the tradition of attending ashrams or think they are important, I would have to refer you to the first answer above.
Some Hindus believe he didn't exist. Some Hindus believed he existed but wasn't divine. Some Hindus believe that he existed and was divine. It all depends on the Hindu that is asked.
believe all that is truth
No. Hindus do not believe in human sacrifice.
Hindus believe in reincarnation.
popular Hinduism belief is that God is everywhere. Thus Hindus believe in all around them.
You become a giraffe. The theist hindus do believe that depending upon one's actions (karmas), one could be reborn as a giraffe. Hindus believe that all living beings have souls. However, not all hindus believe in the theory of 'karma'. I am a Hindu atheist. I believe that with death my personality and consciousness will cease, and the atoms that make up my body will be released and form new associations with a million of things, some living, others non-living.
Hindus believe in the purity of soul and to spread peace and harmony among all individuals.
Hindus, Buddhists and Sikhs believe in reincarnation.
Catholic Ashrams was created in 1988.
Hindus believe god
No, hindus believe the cow is a sacred animal.
For Hindus, the Holy Spirit does not exist, just as Christians believe that Vishnu does not exist.