If you had any problem with your TV, would could take it to a workshop, the technician could diagnose it, query the schematic of that specific model and replace any defective part.
It's is a great shame how many LCD's have been landfilled for want of a part that costs nickel.
But you could fix it if, e.g. a capacitor blew. And capacitors do have a tendency to blow. Thankfully recapping something typically doesn't require a manual, since they are labelled, but you get the point. Repair is important.
I remember those diagrams also didn't include mechanical drawings, so the last part of your comment is right too. You aren't going to be making magnetic read/write heads or even DC motors from information taken from those diagrams, merely the topology of control circuits - which is an opposite view from how we'd see it today.