See page 15 of 34 of the attachment from a recent agenda of the City's Public Safety Committee. Its not intended to put up obstacles to bicycling, but to help enhance the loop road for all recreational uses by keeping southbound Rosemont vehicles out of the 'merging' lane so they have to go to the Seco corner, stop, then make a right turn. The deliniators are spaced to prevent vehicles from going through, but allow bicycle riders and pedestrians/joggers to use it. And I'm pretty sure the City is not focused on 30km/hr bicycle groups, but others riding bicycles at a more leisurely pace for a little exercise.
https://ww5.cityofpasadena.net/commi...ar-Meeting.pdf
Look at the video at about 17:10 when they go through the curve and it looks like some of the riders come close to getting hit by the gray sedan. I'll bet the same thing happens right now when cars use that curve to go westbound on Seco and it results in an occasional fender-bender accident.