For example - in my country gay marriage was made explicitly illegal with a constitutional amendment in 2005.
Many other countries could legalise it with a simple majority vote. But we now need either a 2/3 majority or a referendum. Both of which are very unlikely to pass.
Are you referring to the US?
Many US states passed state constitution amendments (some in 2005) to limit legal marriage and its rights/ privileges to heterosexual couples; it wasn't illegal as in a crime, nobody was getting arrested, but folks were being discriminated against by the government.
In 2010, then-President Obama repeated his opposition to same-sex marriage. It wasn't until 2012 and running for re-election that his position "evolved".
Same-sex marriage was not mainstream until very recently, even in supposedly liberal nations.
I just wonder why do people care about others' sex and marriage so much that they would put that in the very constitution. To me this sounds like a constitution amendment to introduce a dedicated paragraph to ban pineapple pizza. I just eat what I want, have sex with whom we mutually want and share my life with whom I trust, how is my personal choice relevant to anybody else? Okay, if they feel so disturbed they could issue a separate law banning anything but how is this so important they need to put it in the definition of a country?
Presumably less alcohol/less gay marriage is expected to help save people from the temptation toward grievous sins (at least in Christian settings), and help support the traditional family unit in its duties to raise the next generation (less alcohol = less domestic abuse and financial stupidity / less homosexuality = more straight relationships, more children, and partnerships more likely to follow a traditional division of labor & have a woman to raise the children).
I'm in favor of equal rights to marriage, I just think your comment would badly fail the Ideological Turing Test.