accelerometer unequal axes

I am using a MPU6050 and measuring acceleration on the three axes. but the axes don't seem even.
When Z is at 0.5g, X is at 0.8 and vice versa. Same for Z and Y.

I wonder why that is

The best test is to point each axis straight up or down, holding the sensor steady, and you should get 1 g or -1 g in all cases.

If you don’t, you need to calibrate the sensor. A good overview on the process can be found here Tutorial: How to calibrate a compass (and accelerometer) with Arduino | Underwater Arduino Data Loggers

PS: don’t forget your trigonometry, or if you have, review it. sin(30 degrees) = 0.5, cos(30 degrees) = 0.866

When it is calibrated properly, it is PERFECTLY level, and the Z axis is facing up you should have x=0, y=0, z=1g.

your 1g value will vary, based on the sensitivty settings of the MPU6050. if your z reading is 2048 and then you flip it upside down and it reads -2048 then you are likely properly calibrated and 1g = 2048.

A slight tilt in the unit will add or subtract value from the x and y axis.