To keep it very brief:

• the setting is awesome, a fantasy world with lots of lore, because it’s D&D - there has been a lot of lore written about it, even if not about this particular game necessarily. So people are already familiar with how things work
• the company making the game has put out great games in this genre(crpg) with innovative features and engaging gameplay. They have been constantly improving and listening to the community, and don’t seem to be one of the companies that are just chasing the next money-making scheme, as they don’t support today’s P2W or subscription-based models, and even shy away from DLCs, instead opting to give you your money’s worth with only one purchase. They also design their games with replayability in mind and with a pretty big scope, so if you like the game you can easily spend hundreds of hours for that $60. Overall pretty good guys
• not many d&d games have come out recently (some pathfinder ones have been good contenders though), so this scratches a market itch
• the full power of an AAA title for a previously considered nerdy topic. Imagine if comic books suddenly got a 3D movie