Let's remember the OP and get back to the question.
Why is it so hard to get into space? Going into space (on a the generally accepted round earth) requires you to move into at least low earth orbit. To do that you need to travel about 8km/s or 28000km/h. That is very fast.
We are limited in how fast we can move through the air due to its increasingly higher friction as you go faster. So you have to exit the atmosphere to be able to orbit. there is still air some air at 160km high.
Oxygen also reduces as you go higher, this means that an aircraft that uses jet engine can only go as high as the oxygen will allow it to, but at that altitude there is still enough air to limit how fast you can go.
The EU Skylon has developed a new type of engine that tries to combine the best of jet turbines with rocket engines. However I do not see a working craft using this technology anytime soon.
So the best bet is to exit the atmosphere as soon as possible then incline to get to orbital velocities.
The reason why all of that is hard (but do able) is that you have to take all your fuel with you.
The higher & faster you want to go the more fuel you need, which in turn makes you heavier requiring more fuel.
At the end of the day, you need a LOT of fuel to reach 8km/s and that is why going to space is hard.