True Vertical Takeoff and Landing (VTOL) aircraft are complex and expensive. There have been some pretty big ones built over the years. The biggest ones that I know about were the XC-142 tilt wing transport, the Do-31 experimental VTOL jet transport, and the V-22 Osprey. It's quite possible the Soviets built even larger VTOL aircraft given their history of giantism.

Part of the complication and expense comes from the need for safety. For example, the four engines on the XC-142 and the two engines on the V-22 are cross-linked with drive shafts and transmissions to provide power to all of the propellors in the event of an engine failure. The need for secondary forms of flight control in hovering flight as well as normal flight controls for conventional flight also contributes to complexity. Greater complexity means there's more things to go wrong which explains the accident rates for the Harrier, XC-142 and V-22. Being hybrid operations aircraft, they're also more difficult to fly.

There's another issue and that's useful payload. A true VTOL aircraft has a relatively limited payload because it has to lift all of the weight with thrust. That's why Harriers are rarely operated in VTOL mode other than at airshows. Harrier pilots found out a long time ago that for every foot of forward roll they use on takeoff, they can carry an additional gallon of fuel or the equivalent weight in ordinance. That's why the Harriers use short rolling takeoffs and reserve hovering for landings. This mode of operations is called STOVL (Short Take off, vertical landing) and is much more practical. The British Navy took it a step further with their Ski Jump ramps built on their ships. The Ski Jump helps boost the aircraft into the air earlier and effectively increases the runway length by 50%. If you look close, you can see the ski jump in this photo of the USS Invincible. I don't know why the USMC doesn't use ski jumps.