Assalam aleikum Br/ Sr Paglee and all, May this message find you in the best of health and spirits.
Re: "Why multiple marriage at a time for men is allowed but not for women in islam?" I am not a scholar, but in brief my understanding is: life is not only about husband & wife, but also rights of child and child has right to know his lineage. If a woman were allowed to have numerous partners at same time, then parentage can't be ascertained clearly (this is also why women - not men - have waiting period after divorce or bereavement; so that parentage is always clear). My 2p (God knows best). In peace, Rianne PS: just submitted final manuscript to publisher of '199 ways to please God, how to (re-)align your daily life with your duty of care to Creation' (a kind of 'save cash & planet' from Islamic inspiration). Please make dua all goes well.