Good question re: 30 Years War vs ECW. My reasons why I prefer ECW are varied, but come largely down to what I can relate to. I like the IDEA of gaming the TYW, but I find it hard to relate to, to get a feel for. Whilst it's getting easier to find excellent resources to help build up armies and forces, it's still not as easy as possibly it is for ECW. There are countless books in English, regarding the Civil Wars, detailing the nitty-gritty of uniforms, campaigns, colours carried etc, that probably swing many people towards the ECW and away from the TYW, and as these are in English, this is probably why, as you observe, that in the UK and USA, the period is more popular than the TYW.
For me though, as a UK resident, the main reason is proximity. The UK is small, and the Civil wars affected everywhere. Within 5 mins drive, I have a town where a cavalry engagement between 2500 horse took place in1645. Within 30 mins drive, I have a castle where a vicious siege took place, two country houses where more sieges took place, and the town of Newark, where 3 sieges occurred, and Leicester which was stormed in 1645. 50 mins drive sees Naseby. 90 mins drive sees Cropredy Bridge. 2 hours sees Edgehill. Marston Moor, Worcester, and Chester are all within 2 and a half hours. I've visited Auldearn, Torrington, and Landsdowne Battlefields, as well as countless numbers of stately homes and castles connected with the ECW. As a re-enactor, I've fought on some of the original battlefields- even been amongst the first to fire muskets over the Sulby Hedges at Naseby, since Okey's Dragoons did in 1645! ( incredible experience that was).
So to answer your honest and sincere question with an honest and sincere answer, it's because it's close to me, I can relate to it, and I can find information about it easily! That's why I love the period! Hope this helps