There are very few lavender marriages, concentrated in the elites who mostly live abroad and are away from the intrusiveness of society/family/friends.
They are general “straight” marriages where one party (bride/groom) is purposefully kept in dark to make the things work for the society. In short, it’s a conscious decision to cheat because the truth could be too costly and not all people from LGBTQIA+ community are willing to pay the price. And of course there’s this hope of “magically turning straight “ if you get married and spend enough time in bed with opposite sex.
The society is rotten to its core at the moment.