My dad had a hunting area so I grew up living deep in the mountains of British Columbia. Access to our homestead in the early years was by horse or float plane. I am unable to comment on the historical aspects of your questions but most definitely can talk about the logistics.

A horse must have food and water every day. It must be saddled and bridled before riding and your tack must be put away and the blankets dried after each trip. If a wagon or sulky is used a horse or team must be hitched up to it and u hooked after each trip. A respectable person will take the time to rub a horse down and curry comb it after a hard days use. A horse that has been worked hard and is hot needs to have a cool down period before you give it water or it may develop stomach problems. If you aren't using your horse you need to have a pasture or field to let it run and graze in. This means that you have fences to check and mend weekly, if not daily. Horses are living breathing animals with a mind of their own, it is not uncommon for them to get outside your fence and go on a 10 or 20 mile tour requiring you to spend a day looking for them. Only one person should be riding a horse at a time so if their is more than one person you need more than one horse. Horses aren't designed to carry heavy, bulky or awkward loads. One must be creative when moving them. Horses must have a calm and quiet temperament when moving precious cargo such as children - my dad put built specialized boxes with seats and windows, placed my siblings and I inside them and tied them to the sides of a horse when he took my family on trips. Horses are limited as to how much weight they can carry so if you are moving a large quantity of weight you will need a team pulling a wagon or a large number of pack horses. Horses need room to move about, so need more space than an average city dweller's back yard.

Vehicles have keys. They can be shut off and left alone for days, weeks and even months on end and be ready to go right where you leave them when you need them. Instead of having to saddle or harness a horse one simply needs to turn a key and start the engine in order to use a vehicle. Moving more than one person simply involves opening and closing another door. The safety of your children now rests with your driving ability, not the unknown actions of an animal on a lead line.

The final reason why vehicles is our chosen mode of transportation is that a car can be driven 24 hours a day and is easily capable of traveling at 20 miles per hour on the roughest of roads. Horses require rest every day. Tgough there are many instances in the past of people travelling 60 or even 100 miles per day by horse, the horse was almost always dead or near dead at the end of the trip.

Vehicles had an obvious advantage over horses when they first came out. They suffered from the lack of a usable road network, but as more vehicles came on the market more roadways were improved to accommodate them.

I just finished reading "The Range Men," an early history of Alberta by L.V. Kelly. In this book he tells us that unbroke horses taken off the range and shipped to Toronto and Chicago and sold for prices of $125-$250 per head in 1905. Theses prices raised to $400-500 per head during the First World War. These horses we unbroken and unusable until they were trained to accept a saddle or harness. So a broker that bought a green horse would have to train it and pay for its upkeep for at least a week if not longer before he could sell the animal. This increased the cost of buying one to the end user.

By 1908, Henry Ford was selling his Model T's for a little under $900. The cost of 2 or 3 well broke horses.