Well, I can only offer some observations without conclusions. How the game decides what tasks will show up and what value they take on is a complete mystery.
However,
Alex posted her observations about the maximum Relay Tasks you will see.
Now some of my observations seem to say that not only is there a limit to the number of relay tasks at any single time but that the number of other 135s affects it as well.
Last week, we did an "all relays" race just for fun, we consistently had 3 to work on at a time which is consistent with Alex's numbers given our team size. During that week, we dumped all non-relay tasks, including any 135's that showed up.
This week, we decided to do a "mixed relays" aka "mostly relays" so we left the 135s on the board for those who didn't want to do the relays. Now we only ever saw 2 relays (same team size) but up to 3 additional 135s. We never saw more that 5 total 135s + relays. Every now and again when the 135s were scarce we'd see a 3rd relay. And we sometimes saw 4 or 5 135's and no number of refreshes would yield a relay.
We know / think from other posts that the number "high value tasks" (which include 135's) have been limited for some time now and it wouldn't be surprising if a "relay task" would also be considered a "high value task" too.
So how your co-op is treating the 130+ tasks is probably affecting how many relays you'll see.