Peepal is still worshipped like God. Why? It is because, since the ancient times we had known that Peepal is one of the few trees that gives off oxygen even in the night time, thus, to protect this life enriching tree, we related it to God and religion.
'Peepal' tree is almost useless for an ordinary person, except for its shadow. ‘Peepal’ does not a have a delicious fruit, its wood is not strong enough for any purpose then why should a common villager or person worship it or even care for it? Our ancestors knew that ‘Peepal’ is one of the very few trees (or probably the only tree) which produces oxygen even at night. So in order to save this tree because of its unique property they related it to God/religion.