N1 is a simple parameter that's far less prone to measurement errors than EPR. For EPR, you need highly reliable inlet and exit pressure measurement - including probe heat for the inlet probe (and the electrical power required for probe heat is significant - around 500-600 watts per engine). Further, heated pressure probes have still been known to ice up and give erroneous indications. With N1, you need to measure the rotor speed anyway so no additional instrumentation is required, and it's a simple, highly reliable measurement.
Newer EPR engines not only cross compare inlet pressure with aircraft total pressure, they calculate a 'synthetic' exit pressure based on other engine parameters, and if anything is out of a fairly narrow tolerance, the FADEC invalidates EPR and you set thrust based on - that's right - N1.
Now, there are some advantages to EPR - assuming it's accurately measured it correlates a little better with thrust then N1 does, and it's not as affected by high humidity as N1 (N1 power setting charts basically have to assume the humidity is very high - which can make a meaningful difference in thrust at high ambient temperatures and humidity. As a result, N1 rated engines need more margin and tend to 'give away' a little thrust relative to EPR engines (i.e. an average N1 will give you a little more thrust than an EPR engine at a specific thrust set). EPR for a specific thrust setting is usually independent of temperature - so for example takeoff EPR is a constant below the corner point temperature - where as N1 varies with temperature due to that messy "root Theta" term to convert Corrected N1 to Physical N1. With fan damage (e.g. birdstrike), N1 goes up while thrust goes down - EPR engines are much less affected by that issue.
It's worth noting, aircraft have crashed due to EPR measurement errors. I can't think of any that have crashed due to N1 measurement errors.