I'm not sure if you actually know how Blast works. It has nothing to do with exclusivity as 7 teams will all have to play 5 blast events in 2019. Nothing more, nothing less. And if you didn't know, these teams include Astralis, Liquid, FaZe, MiBR, Na'Vi, C9 and NiP
As for astralis prioritizing. Lets make a list of big events in first half of 2019.
IEM Katowice 2019
Starseries i-League S7
Dreamhack Masters Dallas 2019
ECS Season 7 Finals
EPL S9 Finals
ESL One Cologne 2019
They have or will attend 4 of those 7. 2 of them they didn't or won't attend since they're in east-asia and Oceania respectively and they stated last time they were in sydney that they probably wouldn't return there because of the long travel times, the time zone and device's condition.
That leaves one big event that they won't attend and that is dallas which is ending 4 days before ECS begin. And ECS has been considered a big event for quite a while as well and is an event that they regularly attend and have won twice in a row. AND it is on the same continent as them. Why in the hell would they attend dallas over ECS. Sure, the ECS field looks a bit weak so far but thats not the fault of astralis. Usually ECS has a lot of top teams. Last year they had 7 top 10 teams attending out of 8 attending teams.
And regarding the rfrsh situation, sure. It is not optimal. It never will be but try to remember that ECS is run by passionate fans of the game. First, they wanted a csgo team and they got it. They got several actually but they had to sell the other ones in order to comply with rules. And as a big organization who wanted to spread the love for esport to a wider audience they made their own tournament with their own unique take on csgo. Now why would you throw away one of your own passionate creations.
Anyways, it's more like their sister company having a tournament. It is two branches of one organization. Its only about having the top teams at their tournament. When astralis stop being a top team and they're in the same state as VP was 6 months ago they'll stop inviting astralis. Same as when they didn't invite heroic for Blast Pro Series Copenhagen 2017.
And as I said, it isn't optimal but I'm fine with it since I don't think it'd be fair if we asked them to give up one of their 2 main passionate creations.