Lego are just like those brick. If you just pile them on you have no strength, if you interlock them you have strength in one direction, if you have 2 rows interlocked, you have strength in 2 directions.

Imagine a posterboard, one of those 3 section things you can by at a supermarket kids use in science fairs. What happens if you attempt to stand that posterboard up with the sections in a strait line? Now take the outer two sections and place them at an angle to the central board. One will fall over by itself. The other will stand upright and even take a non-trivial amount of downward pressure (weight) before it falls over.

It works the same way with any thin and tall building, it needs to have support perpendicular to the main body. You'll note that most straight brick walls have thicker "towers" at regular intervals. Or it needs underground support, like concrete in the ground for a fence post.

Unrelated: Go buy a lego set! If you've forgotten the joy of LEGOs I encourage you to rediscover it. The kinds of sets they have available these days are vast and the cleverness of their building techniques needs to be seen to be appreciated.