Why don’t they fly to Mercury. What they fear or fear

In the entire history of mankind, they flew to Mercury only twice, and there are practically no plans for the next missions there.

Why is it so difficult to get close to a planet relatively close to us, or is there another problem? Maybe there is some danger at all? The fact is that the gravitational effect of the Sun discourages any desire to send ships and probes there. Mercury’s orbital speed is much higher than that of all other planets in the solar system.

When approaching the Sun, the spacecraft is at maximum speed, and the Sun simply pulls it in. Reducing the speed to enter Mercury’s orbit is an almost impossible task for modern engines. To move to a trajectory to the orbit of Mercury, it is necessary to move in an elliptical orbit around the Sun in order to be close to the planet, not to mention the numerous maneuvers of the ship.
It takes years to reach the orbit of a planet close to us. This means that the spacecraft must be the most advanced and technologically advanced in order not to fall under the gravity of our star. Moreover, it is necessary on Earth to select a launch window, which is very limited, due to the large deviation of the orbit of Mercury. And to fly up to the orbit of Mercury is not an easy task.
The mission should involve a lot of specialists, which makes the project economically unfeasible, since a huge amount of energy and fuel is spent by spacecraft, as well as time and money. Mercury is the only planet in the solar system that constantly shifts its orbit. Unlike asteroids, whose orbital variability is scientifically explainable, Mercury deviates much more, which does not quite fit into the law of universal gravitation, or at least raises questions.
Einstein would explain it as follows, although Mercury is in space, but only at the present moment in time, and time and space are changeable. This means that the theory of relativity works, and we have too little knowledge about Mercury.