Can any military hardware enthusiasts explain why mechas don't exist IRL?

Can't use two melee weapons now?

How are you guys still playing the game? There's literally 0 new content or anything worthwhile beyond 1 play-through.

1. Who are the stealth mechs who attack the player in Investigate BAWS Arsenal no. 2 and other missions? 2. Why do Rubicon Research Institute Weapons attack the mining ship in Escort the Mining ship? 3. Can someone explain the Coral Release ending? I'm assuming that Raven and the other humans become fused with the Coral akin to Ayre, but I'm unsure. Why does the ending scene feature several pilots inside their mechs? ...

Compared to Souls-like games, difficulty ranges from extremely easy to extremely hard from mission to mission, with a few bosses being noteworthy for being hard even by FromSoftware standards. I honestly still enjoy the game and have no real complaints about the difficulty, though I can see how casual players might get frustrated when missions have been relatively easy, and suddenly there is a huge difficulty spike....