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Ty! I think I got it now. I also read upvoting comments is not so good? I’m still trying to figure out why my numbers decrease? Why or how voting power diminishes too?

Upvoting/downvoting comments is fine too, it's part of the system. Every time you upvote or downvote, your voting power is reduced. It replenishes at a rate of 20% per day.
Read more in the FAQ https://steemit.com/faq.html#What_is_my_voting_power

I don't think so. Isn't it natural for folks to be naturally biased towards their own material? Would that not make this practice counterintuitive towards content quality which would invariably affect the perceived value of the platform. If an author believes that their content adds value to the block chain, is all this self-voting and vote buying really necessary?

The self-voting has been an endless debate. There are pros and cons. In my view, when authors spend time researching, creating and writing content, they should have the right to upvote it, and that's what the platform allows them to do, so why not do it? Of course, if they chose not to do it, it's their prerogative. Naturally, if self-upvoting is done in an abusive an repetitive manner, other users have the option to downvote.

The self-voting has been an endless debate.

It will continue to be so until something changes. I'm afraid flagging is not enough for this problem.

Unfortunately, it is a mechanism that is indiscriminate towards any of the criteria you noted and there are not enough people flagging the problem of content that is overvalued due to excessive vote buying and self voting. It's just the nature of the beast right now.