why are we using camshafts?

Because the system we have works well enough. The system is very simple and durable. Combined with smaller valves in multi-valve engines they won't float for any reasonable RPM application (Honda uses them up to 9000 RPM)

One common misconception is that valve trains rob large amounts of power. This is untrue. Yes, it takes force to compress a valve spring, but this is stored energy and is released when the valve is closed. In fact, much of the energy to open the valve often comes another valve that is closing.

Some engines use direct connection for the valves, like on the Ducati superbikes. But this type of system requires a ton more maintenance to keep valve clearances correct and has proven to be unnecessary in many equivalent engines. F1 engines used conventional metal valve springs for up to 12000 RPM. They now use functionally similar pneumatic springs which allow RPMs to approach 20,000.

Directly connected how?

You would still need a mechanism to open and close the valves at the proper time.

The current camshaft system is the simplest and works well.

Some companies manufacture an engine that uses an additional pushrod to close the valves instead of relying on springs. Examples include the Mercedes-Benz W196 and Mercedes-Benz 300 SLR race cars, and most commonly, modern Ducati motorcycles.

These systems, of course, are more expensive to maintain, and is still driven by a camshaft..

Have you ever looked at a piston connecting rod? It's a pretty beefy chunk of metal. Now look at the size of a valve stem. If it was direct connected it would bend and would not respond anywhere near as fast as a spring loaded valve.

There are racing engines that do not use camshafts. The valve are operated by solenoids. The reason they are not in everyday use is the expense. OH and for ScooterB. Mazda didn't invent the Rotary engine, That was from Germany-hench the name Wankel

whydont you redesign the combustion engine and find out.. there is one engine that doesnt use pistons or camshafts , and thats called the WANKEL ENGINE from mazda

formula 1 engines have that some supercars too/

its very expensive and when it goes wrong its always catastrophic, so not used on domestic cars.

too many moving parts causing more friction more drag less horse power