Well maybe the whole thing about dinosaurs sounds silly, but consider this...
Slavery as an institution exists in Amarr. That really changes everything about Amarr society. The slavery is enforced by the Church, who deems it an essential procedure and step towards enlightenment. That means anything which is a 'labour saving device' is depriving a slave of their labour, and thus towards spiritual enlightenment.
When we are thinking of religion here, let's compare the Amarr with the Amish. In Amish communities, contrary to what many people believe, they all vote on whether a technological device should be permitted into their communities or not. Generally, the consensus is that internal combustion engines are bad, but telephones and internet are good.
Since the Theological council would likely be similar to the Amish councils, do you think that a labour saving device such as an automobile would be permitted in Amarr societies?
Let's imagine for a minute that they are. Would you like your slave to drive you to the store? Would you let your slave fix your brakes? Will you pack your slaves in the trunk of your car as you head downtown?
Having a slave society is as much work for the Masters as it is for the slaves. You have to constantly find work for that slave to do. 18-20 hours a day, you must remind that slave that your wishes are the most important thing in their minds. That means constant surveillance and constant activity. Slaves are expensive to buy and keep, so their existence must be justified.
In a Caldari society, the Caldari would invent a labour saving device and think it was clever since it saved a certain amount of job hours, and hence money. A Conservative Amarrian would be abhorred by such a machine, since by replacing the work of four slaves, it only means four slaves are now farther from the enlightening path of a few decades of forced labour.
So, I can definitely see the Theological council forbidding the use of something like a backhoe, because it would deprive hundreds of slaves with shovels of their opportunity for 'enlightenment'. I can think of no better example of bureacratic corruption than the theological council refusing to give their blessings to some machine part made by machine in a Caldari factory, and not by hand.
Look at how Amarrian society is described in the prime fiction again. 'Slow and plodding, like their ships'. A patchwork. Diverse. Deeply religious, with potentially thousands of sects. An empire spanning thousands of planets and countless number of indigenous populations. It's also a Feudal society. Empresses, Kings, Knights, Barons and so forth. It states in the Prime fiction that after the collapse of the EVE gate, Amarrian society reverted back to as far as the bronze age. That means that Amarr would have gone through a medieval period, likely with spectacular churches and so on.
The population of the major planets on ALL worlds is overpopulated. Jobs are scarce. Amarr slave owning worlds have the additional burden of making sure that NONE of their slaves are ever 'unemployed', even if it means doing road cleaning or road repair.
In a society where religion was of such central importance, I think that walking would be more important than automotive transportation. Shrines, relics, sacred groves and the like, don't seem like the sort of thing someone would want to rush by.
AS far as the Amarrians settling on an earth like, habitable planet that was still in it's dinosaur age? Why not? The EVE gate is on the other side of the Universe. The Amarr empire spans thousands of planets and hundreds of thousands of indigenous cultures. I think 'dinosaur taming' would be a good background reason why the Amarrians sought slavery as their main means to problem solving. It would certainly look futuristic, and alien and bizarre.