As we all know
I bet more than 95% of adults stopped on the street in native English-speaking countries would say no to the question "do you know about causatives in English grammar?".
why causative here?
It's not a causative. Dictionary.com and wiktionary.org show 26 different definitions for the verb "have". There are many alternatives to the causative form of the word.
In this case:
To experience, go through, undergo:
We had a hard year last year, with the locust swarms and all that.
He had surgery on his hip yesterday.
I'm having the time of my life!
Also similar to this:
Used to state the existence or presence of someone in a specified relationship with the subject.
I have two sisters.
She doesn't have any friends.
I have a really mean boss.
And what is the difference if I say:
A lot of people ask me if it's possible [...]
Approximately the same. No difference.