You have to understand that when the OG was released, and for a few years after, clerith was the preferred ship and cloti was the underdog. When asked about who Cloud loved, Nomura who didn't give a rat's ass about it, made an half arsed reply about it which led people to believe that clerith was canon for *years*. It came to such a point that, when AC was released, people did *not* believe that Cloud and Tifa were a couple. The fact that the ending showed Aerith in a field of yellow flowers watching over Cloud running errands on his motorcycle did not help that view, so people kept fighting over details. Then they released the On the Way to a Smile novels and... people began to turn around. Because CoT, especially, but other novels too, were clearly depicting Cloud and Tifa in a relationship. But there were still a lot of fights over details.
It was then that Crisis Core was launched, and Zerith became a huge thing. At that moment, it did also help propel cloti properly in the not so underdog ship to the main Cloud ship, since people who loved Aerith and wanted to ship her had a true love ship for her. Then came ACC with the re-release of the novels too, with Cloud's motivations made clearer, with Aerith being erased from the fiels of flowers (it is to note that the devs had put her there because they hadn't shown her a lot in the movie, so they wanted to just add some fanservice and it came back biting them). A lot of Ultimania also were released and bluntly said that Cloud and Tifa were an item - roughly, they share their feelings without words under the Highwind, etc.
But, by this time, people had already fought 10+ YEARS over the LTD. And some bad blood had been drawn already. Pure lies had been told, especially from the other side that relied on bad translations and make up interviews - this was a time when internet was less spread, people who were able to read JP were few, information was scarce. These people to this day still are in the fandom and trying to influence some side of it. Still spreading lies, as you could see in that YT comment section (seriously don't read there, it's a cesspool). But it's why the shipwars are so toxic, because it's been going on for so long that it forces people to be really divisive. Even when you say that Cloud loves both and it's a matter of preference, you are distorting the story and Cloud's character, IMHO. Shipping clerith is fine. I think it works well in AU setting. In game? Not so much, and a few people really hate it when we put them in front of their contradictions and lies.
And that's how the LTD has became one of the most toxic FFVII fandom has ever created.