According to new theory the faster a mass moves the smaller it gets. Its vely vely simple

The speed of light in a vacuum is a constant.

To keep this true for light viewed from reference frames that are in motion relative to one another, length contracts and time dilates. That’s how the universe works, and science addresses this.

WHY the universe behaves in this way is not a question that science addresses.

I'm going with the "why" being simply "because that is how this universe works". It could be different, but it isn't. Physicists tend to talk about fundamental constants that affect how things are, but the essence of the issue here is simply that the fundamental constants of this universe are such that the limits that we face are the ones we face instead of some other possible variation.

Of course, many of those alternatives would not be likely to have life for various reasons, so we basically only have a limited range of realities that we could inhabit, because if reality were not very close to what we have, we wouldn't be here to talk about it because that reality would not permit us to be. Our very existence constrains what the nature of the universe must be, in a logical way (we do not make the universe, we simply cannot exist except if the universe has a certain range of conditions, so if we exist, then the universe has to be within that range).

Because the the closer things get to the speed of light IN A VACUUM the more the MASS of the of the object increases to the point that and intite amount of energy is required to keep the mass accelerating closer to the speed of light IN A VACUUM TIME DOES NOT DILATE and length DOES NOT become shorter for the object that has mass. that happens ONLY FOR THE OBSERVER that is NOT moving at the same speed as the object..

You CANNOT move a mass to the speed of light IN a VACUUM because it requires INFINITE energy and that is impossible..

"Why" is rarely profitable. The theory was created to explain, describe and predict from the KNOWN measurements that the speed of light was invariant from the velocity of the earth at the moment.

If the speed of light is invariant then nothing can approach it, reach it or exceed it.

Because no matter what speed you attain ( relative to the earth ) you can never get closer to the speed of light.

That was what pure observation showed us..

Everything else is our attempts to understand this.

Time and space measurements are not the only things that depend on relative states of motion. Many quantities in physics are represented by vectors who’s components also depend on relative states of motion. So, just as we use the gamma factor - which approaches infinity as relative velocity approaches the speed of light - for time dilation and space contraction, we also have to use the same gamma factor on the components of vectors.

We perform these gamma transformations on something called the 4-momentum vector. Three of the components are space momentum and one is a time component of momentum. Each of the components of the 4-momentum is multiplied by the same gamma factor as time and space, and those components approach infinity as velocity approaches light velocity. Since energy in relativity is a combination of rest energy and the energy due to momentum (in a slightly altered form), we see that both relativistic energy and relativistic momentum approach infinity as relative velocity approaches the speed of light.

Based on the above we can look at it two ways. If relativistic energy approaches infinity as relative velocity approaches light, then it’s obvious we need a source of energy that approaches infinity. We can also look at it from the perspective of relativistic momentum approaching infinity, meaning incremental changes in momentum must require a force approaching infinity.

Please note that there is no such thing as relativistic mass increase. It can be shown that rest mass is an invariant unaffected by velocity. Relativistic energy has a mass EQUIVALENT, but that is not the same thing as an actual physical mass increase of a relativistic object.