Many pistols have safeties and/or hammers that can be easily set to an unsafe when carried like this, if you bump into something or even lean the wrong way.

Theres also the chance of blowing your genitals off or shooting yourself in the hips, upper legs, in a way thats fairly likely to paralyze you or kill you from blood loss from shooting your genitals or femoral artery, if you manage to disengage the safety and also pull the trigger, or draw the weapon improperly in a state of basically threatened panic. Statistically this is rare, but it has happened more than once.

Imagine sitting and then standing and then sitting again with your gun like this.

Ok, now imagine walking or jogging or running and then stopping suddenly. Or even leaning over to reach something.

In addition to being just very uncomfortable with a gun digging into your stomach and crotch, probably the actual main reason this is stupid is that it just is not actually secure, the gun is likely to accidentally fall out and not go off, but scatter across the floor and scare the shit out of everyone nearby.

In ... most (?) of the US, its probably accidentally a crime (brandishing) to even accidentally reveal a concealed weapon without an imminent threat to your person, though this will vary greatly by state, locality and the situation.

Holsters exist to solve this problem.

The closest thing to this that people actually are Appendix Inside Waistband Holsters that clip onto a belt, and go under an overshirt, but over an undershirt, or what are called Belly Bands for non belted people, those are basically underarmor style waistbands with shaped pockets.

In reality these are generally fairly uncomfortable for most people I've ever known that carry a gun on a regular basis.