Both Libra and Taurus are Venus ruled. Both are more amiable,pleasant and slow to anger or extremes of emotions-preferring to keep things on an even groundBecause both tend to project the more extreme nature of their emotions, its no suprise really that they can both attract more forcefull companions.
Libras more open-ended nature may draw the forceful and assertive (Aries) nature of their companion to the surface.
Taurus' relaxed,unhurried,thorough and self-assured approach attracts complexity, depth and attention seeking tendencies from their companion (Scorpio)
Taurus however focuses on material security/physical stability. So the partnership will highlight issues of potential loss of that materialistic security,deaths sharing of resources/trust,power struggles and extraneous circumstances that may topple that stability/enhance personal power(Scorpio)
The Libra hones in on the more inclusive/relations centred part of partnership. The needs of "we" and inclusivity are important.
So the partnership will zone in on issues of overdependency, unreliability of associates, separation anxiety and associates making decisions unilaterally/bullying. These guys may attract someone who acts single though in a partnership(Aries)
On the surface, both attract more forceful partners that seem more dramatic than they(Lib/Taurus) are. But the nature of the relationship differs in themes surrounding it.