Why does this take so long ?

Plain old 18-week strain aside. Phenotypic plasticity. Floral transition can be affected by a multitude of factors; too much or too little nitrogen can mess up gene expression and signal triggers. Nitrogen acts not just as a building block, but as a direct signaling molecule. It intricately intertwines to control when a plant transitions from vegetative to flowering. The Florigen gene and its rate of expression are highly sensitive to immediate levels. Nitrogen directly fuels cytokinin and auxin production, which dictate whether a plant allocates its energy to leafy vegetative growth or axillary bud and flower development(bud leaf ratio). Judging by the looks of your plant development, it looks to have a consistently high nitrogen ratio, which may be skewing developmental patterns. Then again, landraces often look different too. The ratio of ammoniacal nitrogen NH4+ to nitrate NO3- is also a critical determinant of a plant's developmental timeline. Controlling this ratio alters internal signaling—nitrate promotes structural growth and can act as a floral signaling molecule, while ammonium pushes vegetative energy and affects cellular pH. As the photoperiod or environmental cues trigger flowering, most crops perform optimally by shifting to a highly nitrate-dominated diet. Keeping ammonium very low (around 5% to 10% of total nitrogen) in late flower prevents toxicity, stabilizes the rhizosphere pH, and ensures the plant directs its remaining energy toward floral ripening rather than green growth. Similar to "stress tolerance" in that it invokes a response, or it doesn't. Too strong/many of the wrong signals tip some over the edge into "indecision", and can take forever to transition. Remember, plant genetics are not entirely dictated; they are complex combinations of genes 50% and environmental expression 50%, meaning the direct availability of nutrients/spectral composition dictates the developmental structure/ratio and phytohormone balance. Incorrect signals can strain development. Sucrose (carbon sugars) in a medium is much more than a simple energy source; it acts as a core signaling molecule that harmonizes carbon status with cues to initiate flowering. (be warned of using sugars tho, very strong oxygen scavenger that will cause direct competition between microorganisms and plants for oxygen if it's scarce. Sucrose is far more a signalling molecule for plants than glucose so it's important to distinguish and not just feed "sugars" to a medium unwittingly. An increased ratio of reds at 660nm strongly promotes flowering. Add 15-30 min of 730nm at sunset for maximal signal induction of florigen using the Emerson effect. Best of luck. Looks like you got your hands full with those beauties!