You assume they didn't rule it out and never investigated this angle. Investigators work with the physical evidence since it speaks loudest. It wasn't terrorism because neither Estonia nor Sweden had pissed anybody off in 1993, and neither country is a threat to its neighbors.
In that weather?
Why can't it be simple crew ineptitude? I ask only because it seems like it was. The vehicles were loaded incorrectly distributing weight to one side, and then the bridge crew failed to slow the ship while they investigated the loud noises below, meaning the ship was slurping in water at a high rate.
Charged and convicted are two different things. The US Navy has a sorted history with prosecuting innocent sailors to cover for systemic problems. The USS Iowa incident is a glaring example. The sailor will have his day in court and we'll get to see the evidence.
Should point out that the ship was moored to the pier, not out at sea in bad weather.
And yet it wasn't the first time this kind of thing had happened. MS Herald of Free Enterprise capsized for the same reason. in 2014 MV Sewol sank when a sudden turn caused the cargo to shift to one side. I'm not quoting anybody. I own a small pickup truck, when I haul a heavy load I need to know the weight, and I have to distribute the load and tie it down so it doesn't shift. Pickup trucks and ferries share the same proclivity to roll over.
You are kidding right? This was in the era of the fall of the Soviet Union, which it very much resented. The Berlin Wall came down, Latvia, Lithuania, Estonia, Belarus, etc,. all former so-called 'Baltic states' (= read Soviet bloc). The Soviets did not like it one little bit, especially when the Estonians wanted to expel the Russians from Estonia. Many live in Narva, and the Russian response was that to get rid of them they would have to make Narva a part of Russia. The old Stalinist-appointed officials were now replaced by Estonians. It is believed the area around Narva is heavily Russian-mined.
The KGB were being replaced by a CIA/MI6/KSI friendly intelligence agency. The soldiers in the Russian army had no idea when it would get their next wages, so the wholesale selling of Soviet military stuff began to take root, with the Russians selling submarines via army agents. There will certainly have been ex-KGB men, such as Vladimir Putin, who would very much disapprove of Soviet/Russian state secrets and space programs being smuggled out on the black market by and handed over to enemy no.1, the CIA, of whom Bildt is said to have been an agent. You very much cannot rule out cold war shenanigans, especially as the
Estonia passenger ferry had been used for this very purpose, presumably, with the belief the passengers were acceptable collateral damage/human shield.
The weather was pretty standard for the Baltic in late September. Nothing unusual. They would have known of the expected weather conditions and been prepared for them. For example, lashing down heavy lorries tightly.
The very fact that that sailor has been charged, even not yet convicted indicates that you can't take a sailor's word at face value in an accident...as that sailor might have caused that accident!