They seem to come and go for me. Sometimes I'll get nothing for weeks and then i'll suddenly get two the same day.

I feel like I've gotten more recently! However, it may just be that I've been on more because of Lumi. I'm not quite sure which. XD

Given that subeautique invites are a random event based currency, it's more likely that your activity on the site has increased. Typically, I find myself gaining more subeautique invites and other event based items when something on the site causes me to spend more time online. So I wouldn't necessarily say that they've become more frequent, at least in my experience.

I haven't gotten one in a couple weeks now. ;( Wondering if it is really that I am playing less or did the frequency slow down too?

a lot of Subeautique items got dropped into the economy via the Free Shop so there really hasn't been much need for them and the price dropped a bit. Invites prices are sporadically supported by TPTB so it seems likely that the drop rate has lessened over the last month to make up for this drop in price.

In two days several lines will retire. Me, I've been accumulating mine since I have all those already even though the drop rate does appear to be less. I will be spending them soon because when the retirement happens my creaky slow self may score some of the newer items that have been stubborn in dropping sP price in user shops.

If you have your eye on some of the newer pieces and since you've been unlucky you may want to buy a few now.