Because everything happens there. It carries the whole leaf, every push and pull twists it, and the seal has to remain effective along an edge that is constantly moving.

A door that has dropped, binds on the tray, or leaks down one side is almost always telling you about the hinge stile rather than about the glass.

That is why hinge quality and how they are fixed to the wall or the fixed panel is the thing worth paying for on a hinged door.

The full width of the leaf, because unlike a pivot nothing swings back inward to offset it. This is the price of the simplest and widest opening.

In a compact bathroom that is frequently the deciding constraint, and it is why bifold and sliding doors exist at all.

Where the space is there, a hinged door is the easiest to walk through, the easiest to clean and the one with the fewest parts to fail.

Outward, in almost every case. An inward-opening leaf drips onto the floor when opened and, more seriously, can be blocked by someone who has fallen inside.

Outward opening is standard because of that, and is effectively required wherever accessibility is a consideration.

The exception is a very large wet room where an inward leaf costs nothing and keeps water off the floor, but even there the access argument usually wins.

Yes, and the upstand height has to be allowed for so the door clears it through the whole swing rather than only when closed.

A door that catches on the upstand as it opens has usually been hung too low, or the tray is not level, and forcing it wears the hinges quickly.

Setting the door with a deliberate gap at the bottom and relying on the drip seal to close that gap is the normal approach, rather than fitting the glass tight to the tray.

A magnetic strip at the leading edge, meeting either the fixed panel or a matching strip on the other leaf in a double door.

Because the leaf is heavier than on a folding door, the strip has more work to do, and a hardened or distorted strip shows up sooner as a door that will not stay shut.

If a new strip does not fix it, the next thing to check is whether the enclosure is plumb, since a leaning frame makes the door swing away from closed under its own weight.