Because it may become inappropriate as he ages. It's not good for your son to be too attached to you, especially physically, because then he won't grow on his own and found his own family and life. He will be too in love with you and eventually eschew proper social life in favour of wanting to marry you or permanently remaining in an early stage of your relationship. This isn't good for either of you.
At the same time, restrictions may be taken as rejection and be bad for him (and down the line, you).