Several reasons:
1. Size. I can easily move the Electron SEs around in the room by myself. I will also be retiring in a few years and don't want to deal with speakers I will need help moving.
2. I wanted the upgraded internal wiring, and these came with it (DI is $300 extra).
3. I wanted gloss black finish and it was only $500 extra (DI is $1500 extra).
I am not a bass head, so I figured the 8" drivers would provide enough for me (I was correct).
The Electron SEs cost me about $3600, and the DI would have cost me $4800 and the DI SE would have been $5600. It's not really about the budget, though, as I can afford to buy even the Ulfberht, but more about not knowing where I will be after I retire, and I can always sell my current equipment and buy new when I move.
I have never heard any Tekton Design speakers, so it was a leap of faith that what I have read is accurate. My previous speakers were horn loaded and I liked the more life like attack of percussion and plucked strings. I spent the middle of the 1990s looking for replacement speakers that could deliver, and failed to find them. Most high end speakers back then were more into reproducing bowed strings and lacked the dynamics I am talking about. I almost purchased Von Schweikert Research VR-4A, but they were $5000 and I didn't think the attack was quite good enough to justify the spend.
My previous speakers were JBL SVA-1800, and I loved how a good rim shot would make you blink, just like if you were standing near the drum set (I have been an amateur musician since age 4, so I know what live instruments sound like). These new Electron SE that I just received this week are also very good at attack dynamics, but also the sound is blended well from top to bottom, so you can't hear a difference in the quality of the sound like you could on the JBL between the horn tweeter and the 8" woofers. There is also better detail in the bass, with richer timbre of acoustic bass. The resonance inside the piano in the lower registers is also richer. I will need to live with them for a bit longer to develop opinions about what other aspects of the sound are now better.
My top 3 upgrades have been:
1. Yggdrasil - Better separation of instruments and just plain ease of delivery over the multibit card in the Ragnarok 2).
2. Tekton Design Electron SE
2. (tied) Aegir - Bigger, more coherent sound stage over Ragnarok 2.