Why top players have disconnected walls in core?

That depends.

The example village, it is, like Momo said, either to hide traps, or to distract troops away from the town hall, and towards the junk buildings, pretty much guaranteeing a 1-star loss, instead of a 2-star. The placement here shows he doesn't want anything spawned in the middle

In my village, however, I disconnect walls to funnel troops into traps and splash damage, a common tactic, but uncommonly mastered.

Town hall 11 villages are essentially indestructible. What I mean is, you won't get a 3-star if you paid to flat out win.

Does it work for town hall 10? Somewhat, but I would more focus on the funneling, rather than the waste of space shown above.

Should you use it when trophy pushing? If you are pushing above 2800, yes. Otherwise, no. 2800 separated the men from the boys when it comes to attacks.

UPDATE I was requested to post my village. Here it is.

My Village:

What the attacker sees:

What the walls are doing:

Critical Info:

• My league is currently Crystal III. Works very well there.
• Tested up to 2800. Prevents 2*s in 98% of occasions, you may even win a few!
• It's a fairly new layout, so naturally, it will need some tweaking.
• It's a trap base. The point is to make the troops have every reason to explore, and none to hit the core.
• My village is rushed. If it works on a rushed village, it works on yours, too.

Critical Trap Village Building Points:

• Hide walls and traps behind buildings, and where the attacker least expects them.

• Make space around the town hall on two or more sides.

• Inferno towers aren't the most important defense, but they certainty do help.

• Cover the core in splash. Use all walls! They don't have to be used usefully, but they have to be attached to your village.

• Always have more than one route to funnel troops!

• Air sweepers should always be slightly overlapping, regardless of rotation!

• Walls are your best friend, and your worst enemy.

• Use normal resource storages as walls, and cover them! They'll be a massive roadblock for the enemy, especially one blinded by greed!

• Leave no more than 6 buildings undefended.

• Place Teslas as a lure for golems, not as a main defense!

• Two Air skelly traps, one ground.

• Build anticipating jump spells, but have a layout for when there isn't.

• If troops are running around "useless" walls, they aren't killing your base.

• Don't decorate your village interior. That's a glaring "Trust me! It's safe!".

• When pushing cups, you need to focus on minimizing losses, not risking all or nothing. Recovery from a 1* is less work than winning a defense, then getting 3*d.
• Feel free to add anything else I missed.