Sometimes when I hear somebody from Ireland speak I don't notice their have a different accent for a few seconds, this includes southern Ireland and Northern Ireland. BTW I'm aware there isn't one Irish accent but many different ones.

When I watch the introduction of these videos, I don't notice much until point out their different pronunciations reading the list. Obviously there is a difference but way less noticeable to me than overseas accents from elsewhere.

Considering that there is a ton of Irish ancestory in North America, is this surprising?

(I am American - or USA-ian or whatever you want to call it)
I was surprised to find the similarities, not just due to 'movies' representing Irish accent distinctly (I don't think I've seen many films featuring Irish) but based on Irish people I've met whose accent was more distinct from my point of view.

About the videos, I would say the beginning part of the guy from Northern Ireland seemed more distinct, while the latter did sound closer to American. The girl sounded close to American consistently thru the video... but the thing is, she explicitly says other Irish people don't think she has an Irish accent, so I don't really think that is good example.

Here are links suggested when I watched those videos, which have more distinct accent vs American:
Girl https://www.youtube.com/watch?v=QBkIrMf7UIw
Guy portraying multiple Irish accents https://www.youtube.com/watch?v=hIeks_F3yOE

The latter may be over the top because he's portraying stereotypes, but Irish I have met did have accents on the continuum of those and the girl I linked. Incidentally, while not super engaged with Irish culture, I always thought it was the nicest sounding accent(s) amongst English accents. The more American-sounding accents the OP posted would not really qualify as especially notable if I had to rate them. I don't know if there is trend for more American-ized pronunciation with modern film/TV and so on familiarizing Irish to American accent?

Eh, I don't think so, at least not completely from my experience anyway.

It's funny how people who live in the UK (tho this is Irish) mock Americans for thinking they all have the same accent yet topics like this do the same thinking the yanks all have the same accent. Brooklyn (pre hipster) sounded different than most NYC people. NYC in general sounds different than Boston. Georgia Southern accent is vastly different than a Tennessee accent. Where I live we don't have an accent at all. There is no singular 'American Accent' at all.

What makes you think you don't have an accent?

There is no North American or US accent. I mean keep in mind:

Landmass of Ireland: 32,595 sq mi

Landmass of the European Union: 1,707,642 sq mi

Landmass of the United States: 3,531,905 sq mi (The Lower 48 ALONE are 2,959,064 sq mi)

The United States is absolutely gigantic. Think of how many dialects and accents are in the British Isles. Same applies, though far more spead out. Georgia sounds different from much of deep Alabama which sounds different from Virginia which sounds different from Ohio which sounds different from Boston which sounds different from Jersey and so on. 

Having said that, Scotts-Irish descendants may have similarities in some areas in the country.

To be fair the amount of accents in the UK is quite uncanny for such a small area of land in comparison to the US. It's honestly something I look to be just a signature and one of the most famous stables of British culture.

From what I've found online is that there are about 56 main "accent types" in the British Isles, but within each of those accent types there are scores or even hundreds of distinctive variations. In comparison there are about 42 recognised accents in the USA with much less town-to-town variation and much more mutual comprehensibility.

I personally have never mocked a group of people for sounding all the same (to be honest I don't get what there is to even mock in that), although every country has a stereotypical accent whether it be American, English, Scottish, Canadian, French or Irish so on and so on that people just associate with each country.

Now that I watched some more videos, it's actually some Northern Irish accents that sound the most similar to American accents.

I'd say though that the differences between American accents tend to not be as different as depicted, especially with the media and internet which I believe is converging dialects. For example, I live in Canada but pronounce many words the American way due to the influence of media.