Don't make me beat you with a SCART cable! YPbPr is a shittier standard. Let's use 5 cables instead of 1, what a great fucking idea.
Unless you're using a frame meister/upscaler or in euro land, most people convert scart to BNC anyhow from what I see in the US unless its a DB25 connector. If you read lots of forum post you see the same problems with the SCART standard: audio buzzing, crosstalk, incorrectly wired (JP21 vs Euro),and finding a good quality scart switch is expensive. This isn't even factoring in SCART can carry every signal to man and it makes it a bitch to find a quality one unless you make one yourself or buy from a known good seller. Individual connectors almost always never have this problem, are more familiar here in the states, and easier to source.
I agree YPbPr is a worse standard in theory than RGBs but I've always preferred individual connections. It doesn't have to be component, I like BNC connectors with RGBs.With this in mind, look at the S-video input on a Commodore 1702 monitor. It sucks we never got that two RCA plug for s-video, but manufacturers went with the four pin all in one that is always a joy to plug in.
tl;dr it just seems easier/less pain in the ass to deal with BNC and recently ive started noticing people are making cables like that now (not just for PVMs either). The cables above are for people connecting to component CRTs and flat panels.You don't need the SCART meme to enjoy RGB goodness is all im saying.
I will say this, SCART being able to automatically change inputs by what is powered on by sensing is pretty cool if your inputs are in a hard ass location to reach.