Gay marriage not legal -> gay marriage legal. You may think it's right or wrong, but it's definitely social change, it's definitely in the left direction, and, from the perspective of 2000 (even more, 1950) it's quite extreme.

Is that it? From the perspective of 1950, giving black people civil rights is "radical leftism."

To social conservatives? The swiftness of things like LGBT gaining moral acceptance. The attack on pronouns, cancel culture that attempts to ruin lives if you have ever done anything in the past that by ever-changing current woke standards is offensive.

To be clear on my stance, I'm left and I am pleased overall with the social changes and tolerance being pushed.

Socially conservative people have always existed, and would typically be wary of changes in the world order/society no matter what. Our society on this planet has changed at a much quicker rate than average. Then throw in social media, which allows amplification of the extremes, and things really can feel off the rails.