Why G23 energy-saving lamps need ballast, does it make sense also for LED type?
I think you're thinking of all light bulbs as just a thing you put 120V on, and then magic happens and light comes out.
Voltage is pressure.  Current is flow.
Not at all. Lights work on current, and most of them need external help to limit how much current flows through the bulb (or else they will flow too much current and explode). Edison's biggest challenge with the incandescent bulb was to get it to work on constant voltage.  Using constant-current was impossible because in the day, that was only possible with AC power, which would've required conceding the War of the Currents to Tesla.
Of course Tesla did win, and the result was discharge lights were viable even before silicon electronics.
So the upshot is that every light source needs some sort of current-limiting device, except for incandescents are able to do it themselves because of Edison's vast search for a self-limiting incandescent.
So yes, fluorescents need a current limiting device called a ballast, that also knows how to run pre-heaters and provide an initial &quot;arc strike&quot; voltage when preheating is done (which takes less than a second).
All the HID lights (low/high pressure sodium, metal halide, and mercury vapor) also need a ballast.  So do neons and traditional arc lights (&quot;Batman beacons&quot;).
LEDs too need a current limiting device.  A resistor will suffice, but if you want peak performance out of them, it really needs to be an active ballast-like device.  Because they're electronic now, they call it a &quot;driver&quot;.
Fluorescent ballasts and LED drivers are not interchangeable and one will not play with the other.
The things on the market that you call LED &quot;bulbs&quot; that have an Edison base are actually a manufactured products containing a) LEDs, b) heatsinks, c) lensing/diffusion, and d) an LED driver circuit.
As far as an LED &quot;replacement unit&quot;, first I wouldn't buy anything from Amazon ever since they became eBay, because so much of it is unsafe junk from the worst overseas factories who cut every corner and ignore safety standards.
But yes, there is such a thing as an LED &quot;fluorescent replacement&quot; designed to work even though the ballast is still present.  This too has LEDs, heat sinks, lensing and electronic driver.   So in effect the ballast feeds power to the LED driver, which is built &quot;smart enough&quot; to behave the way a ballast expects a fluorescent tube to behave.