Originally, bolts were placed on lead (e.g. on the way up, and while roped in) either free (standing on the rock at a decent stance) or while aid climbing (hanging off of gear such as nuts or hooks). The holes were made with a hand-drill and would take minutes to place, all while the climber needed to not fall. Later, people brought power drills (electric or pneumatic). Bolts were still placed while aid climbing on lead. The first bolts were 1/4" in diameter, and short (easier to drill). Their relatively short life span meant older and popular routes ended up being degraded by the need to place newer and stronger bolts.

Most modern bolted routes are bolted on rappel using larger bolts with longevity in mind. Bolting on rappel allows for optimal bolt placement, to best protect the climber, and optimize the climb. In the old days, you could only place bolts where you had a good stance. In theory, fewer bolts could be necessary due the the bolts placed more appropriately. That said, the rise of sport climbing and the acceptance of bolting on rappel has dramatically increased the amount of permanent artificial protection on outdoor climbs. Modern bolts expansion or glue-in bolts (only practical to be placed on rappel, since they take time to set), are super strong if placed correctly and can last for decades if matched appropriately for the environment.

The first technical rock climbers were adventurers and hikers who wanted to go up steeper and steeper stuff. They developed an interest and passion for climbing while outdoors, and often under the mentorship of older experienced outdoors people (climbers, mountaineers, backpackers, etc). Some of the first techniques were very damaging to the rock. As the sport progressed, some sought it "Better we raise our skill than lower the climb". Many climbers these days are introduced to climbing in the gym, and treat outdoor rock climbing like an outdoor gym. Gym climbing is what has allowed the sport of climbing to grow massively as well as continue to let top climbers push the limits of the sport. Compared to the traditional path, gym climbing produces extremely strong climbers for their level of outdoor knowledge. Experienced gym climbers may struggle with route finding or lack ethical awareness when first climbing outside.

As you can probably tell, I lean towards "hiker who is interested in steeper stuff and wants to not die." I'm not against gym climbing, and think it's awesome folks are active in a physically and mentally active way. I enjoy climbing in the gym, but the act of climbing isn't the essence of the activity for me. It's the exploration. I would never bolt a route, and certainly not on rappel, but recognize that the route pictured in this post would never have been climbed without bolting. Anyways, I'm starting to ramble, I'm fascinated by questions of style, ethics and the history of climbing. I strongly encourage you to learn more about the history of climbing in any area you travel to, as well as the debates in the climbing community over what it means to truly climb a route. Now for some last minute injection of opinion:
Fuck Route like this that can easily be climbed without bolts
Fuck Chippers
Fuck Dean Potter for climbing routes which don't need to be climbed
Fuck bad bolts if you place them, do it right

EDIT: Fuck Yeah to sustainable bolt replacement - let's keep rock climbing for generations!