Depends on the manner.
A lot of those promotion videos are designed to make the person promoting look good, rather than actually promote the channel. You have to think about it from the shoes of a big YouTuber. What do you have to gain from promoting a small channel that barely anybody knows about? Nothing.
So you think a big YouTuber is doing it out of the goodness of their heart? Maybe.
However more often than not, it is to generate a sense of "I help viewers like yourself, I'm not like all the other big guys, I care". Which is fine, I mean it definitely beats people who flex on their own viewers (I made a video about guys like that recently).
A lot of those promotion videos are designed to make the person promoting look good, rather than actually promote the channel. You have to think about it from the shoes of a big YouTuber. What do you have to gain from promoting a small channel that barely anybody knows about? Nothing.
So you think a big YouTuber is doing it out of the goodness of their heart? Maybe.
However more often than not, it is to generate a sense of "I help viewers like yourself, I'm not like all the other big guys, I care". Which is fine, I mean it definitely beats people who flex on their own viewers (I made a video about guys like that recently).