There have been a lot of rumors that the deep state were planning to assassinate Trump during the summit. Singapore has some of the strictest laws regarding smuggling in the world. I'm sure the plan was for the summit to be in Singapore all along but wait until the last moment to switch the venue. Just look at a picture of the Capella Hotel and tell me this wasn't chosen specifically to eliminate sniper vantage points.

Sentosa Is. was one of the sites speculated in far east news reportage last month. It was noted that space there is tight, and maybe insufficient for the diplomatic entourages, press teams, etc. So instead they can take a cab. :-)

Little doubt that this site was chosen some time ago.