Sometimes, there’s no single reason. It’s a combination: old pipes, a slightly closed valve, and a neighbor who just installed a huge sprinkler system. Welcome to home ownership. You can chase ghosts for weeks.
Here’s my advice: start with the free stuff (clean aerators, check valves, ask neighbors). If that fails, call a plumber and accept the diagnostic fee. It’s better than buying a new water heater you don’t need.
And hey, if all else fails, move into a hotel with good water pressure. I’m only half joking. Sometimes, a strong shower is worth the price of a room with a rain-style head. You deserve it.