As of January 2018 there were 53,732 commercial ships registered worldwide... (wow!) The oceans are very large...but of course a LOT of these ships need to use very small areas of them... and at the same time. Probably shouldn't be surprising they hit each other occasionally!
Keeping a look out too is a dying thing. Even back in MY Navy days we altered course to pass astern of merchant vessels (at night particularly) because it was quite likely there was no one awake on their bridge... a radar proximity alarm would have been set no doubt ….. but no one was actually up and about keeping watch.... so even as the "Stand On" vessel...discretion was seen as the better part of valour.....
When ships get VERY close to each other too there is a reaction (Bernoullis principle?) that drags them together the last little bit.... that doesn't help!