I started with extract (as most home brewers do) then made a single partial mash batch before jumping over to all grain... It feels like I'm making much better brews with all grain. Of course, I'm also formulating my own recipes, not using kits. Having the level of ingredient control all grain gives you, IMO, makes for much better brews. You know EXACTLY what's inside the batch. You no longer need to guess/wonder about what else has been included in the extract (that you might not want)...
For the question of why breweries use the all grain method... I think it has a lot to do with cost per batch. With all grain, you save a lot over extract. The same batch that would cost me about $16 for 5 gallons as all grain would run me over $55 if brewed as an extract batch. So the cost is about 3x more for the same brew when you go with extract, compared with all grain. Even if you get DME in bulk, the cost will still be higher with extract batches.
Personally, I have no issue with spending the extra time to mash my grains, considering the brew I get from it. Spending the 60-90 minutes for mashing isn't wasted, when you're brewing and bottling on the same day.
If you have a propane burner you're shaving time to get up to temp, and boil, during the process.
You can get into all grain brewing for either a few dollars (grain bags for the BIAB method) a little more (converting a cooler into a mash tun, aluminum kettle, propane burner) or a lot more (full on Blichmann setup), or any combination... IMO, once you have the processes nailed, you can decide if/when you want to migrate to either partial mash, or all grain brewing. There's plenty of information on these boards for different ways to do it...