Why do the Irish say "I suppose" all the time?

It buys some extra time for spoofers to think about their answer to a question.

Out of kindness, I suppose.

The definition…... think or assume that something is true or probable but lack proof or certain knowledge."I suppose I got there about noon"

I suppose I’ll go to the cinema = i probably will go to the cinema.

If I had tickets and definite plans with X… “ I’m going to the cinema “

It's mainly a filler, but I suspect it's chosen over other possible fillers (of which there are many) because it avoids the speaker appearing dogmatic or overconfident, and suggests that he is open to reviewing his position in the light of new information or of arguments he hasn't yet considered.

I can't think why the OP imagines that a politician should never say it. Unless he wants to come across as a second Donald Trump, whose confidence in himself is exceeded only by his ignorance of virtually everything else, a politician would always be wise to appear open to new information or new thinking.

It is used instead of 'I think' …. it might be less sure and assertive than 'I think' and that makes it very Irish - leave some wriggle room.

On a similar aspect I have noticed that GAA players use 'look' to open a sentence and FAI players say 'listen'. That's a totally unscientific observation, but it amuses me when watching sports interviews on d'telly.

It's just natural speech. And in informal writing, starting a sentence with Oh is also harmless. People are seeing problems and getting annoyed by stuff like this for no good reason.

That’s where I initially thought the OP might be coming from when I read the thread title - it being used in response to a statement where the listener really doesn’t give a shìt one way or the other and just says “I suppose” to keep the peace.

“I suppose…” before a statement is just a way of lending support to the statement as if it were actually true. Generally speaking, what follows after “I suppose…” isn’t true, and the appropriate polite response is “I suppose”, by way of keeping the peace. It’s placating the speaker, while not necessarily agreeing with what they’re saying, because it doesn’t really matter.

Generally speaking, and speaking in general terms, I suppose that might be true. Or it could conceivably be a lie.

On the contrary, fillers are an indication that the speaker was listening to your question, and needs time to process it and to frame his reply. That's why you hear them a lot in radio and television interviews.