Answer:
Because given the dynamic nature of Google's auctions, the appropriate bid can often be a moving target that's challenging to reach at scale when using manual bidding.
Explanation:
Above all, the adequate strategy depends on your company's marketing goals. Therefore, it is wise to always take into consideration that first. When manually bidding the auctions, it is important to understand the downside of doing so. The actual bids can vary depending on each situation.
For example, you have determined that a specific keyword is of extreme value for your business, so you set a high manual bid for it. But, what happens when it doesn't get searched for a while or simply gets dominated by a group of complimentary keywords? That is exactly why automated bidding gets more convenient and simple.