What is the problem with rotation?

After further reading of my own books by communicators of the subject, and web sites, I am more intrigued by the lack of reference to the possibility that gravitation is connected to a grand rotation, and that GR defines four spatial and one time dimanesion, total five dimensions.  A lot of maths is being done to limit the number of big dimensions to four, eg the path integral, using complex numbers to convert 3s+t into 4s.

The nature of gravitation does not appear to be one of the outstanding mysteries, yet if this is the case there should be a popularly-understood model of it.  Instead we are being told that it just is.

The conundrum to me is, how are things which are so obviously apparent from our observations and accepted therories not clearly acknowledged?  Specifically:

• just as the bobbles on the surface of an orange indicate the existence of the 3rd dimension (up-down) to a 2-d being, the bending of spacetime by masses shows the existence of the 4th spatial dimension to our 3s+t classical world
• the idea that inertial mass and gravitational mass might be different, and their equivalance to very fine experimental accuracy may still be a coincidence, may be good scientific practice.  But in reality they are clearly the same thing
• a can whirling around on a string experiences fictional centrifugal force, and a body in orbit round a planet is subject to two fictional forces - centrifugal, and the centripetal force produced by gravity.  It orbits forever, with no new energy, and feels nothing!  The two forces are one and the same, and their common cause is - rotation.
• the differences between linear acceleration and constant-ω rotation are that (a) in rotation the acceleration is achieved with no work being done, and (b) an additional dimension is required, namely the axis of rotation
• I have seen it stated that masses bend spacetime, it is implied "just by being there".  But this only makes sense if there is interaction.  You don't dent a mattress standing against a wall just by standing next to it.  You have to push against it for the denting to happen - or it has to push against you.

I suppose the answer to the conundrum is that if time is sufficient as the fourth dimension, there is no need to invent a fourth spatial dimension.  But G appears to have been constant for the last 12 billion years or more, so the shape of time in terms of the radius of curvature characteristic of the whole universe is already fixed.

Maybe easier to assume s4, find its properties, then try to equate s4 with t.  But I do need to find how this has been written up already, in an understandable way.