Just kind of thinking aloud here, but:
Escape is a fantastic idea that was hindered from the start by repetitive map tiles, unskippable and tiresome cutscenes, long load times, and the general lack of rewards by comparison to the other easier, more established PvE mode, Horde. But I think it fills a need for a PvE mode that requires fast pace, coordination and knowledge through experience, all without the typical Horde-style “hunker down and fight off waves” that every shooter has now.
While they aren’t making any more Escape maps, and assumedly tiles, this could be so that they can refocus on how they design maps and tiles for Escape in Gears 6. Remember that games have a long development cycle, and sequels have a transition period where they move developers working on the previous game to working on the next game instead.
Escape might be done in Gears 5, but if the mode is staying in Gears 6-- and I hope it does-- stopping the content now could make for a much better and fresher experience in Gears 6.