Why is it not possible for water to directly attach itself to the alkene to form an alcohol in oxymercuration? What is the need for mercuric acetate?

When going through the preparation of alcohols, I came across the method of Oxymercuration-Demercuration.


[![enter image description here](https://i.stack.imgur.com/rx7v3.png)](https://i.stack.imgur.com/rx7v3.png)


Now, after going over the reaction, I didn't understand the purpose of the mercuric acetate in this reaction. According to me, H2O should be able to dissociate into H+ and OH- and then break the double bond and attach itself to the alkane. But, this does not happen because of some reason that I'm not aware of.


Image source: <https://en.wikipedia.org/wiki/Oxymercuration_reaction>




Alkene is a nucleophile, while water also is a nucleophile so they don't interact with each other directly, so we need something to alter alkene's property. Mercuric acetate forms a cyclic intermediate with 2 carbons of alkene where Hg has a positive charge, so it really needs that bonded electrons back. This makes the carbon site partially positive, thus it now welcomes water and oxygen donates its lone pair to the carbon while the mercury atom withdraws the electron, here the latter process is faster. Thus the process is SN2 where the transition state has a carbocation character, so now we get the intermediate that is shown in the diagram.


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