Question: why maple does not simplify this to what it should be?

I have the following code:

Likelihood := proc (r, t, s) options operator, arrow; product(exp(-(1/2)*((rr(k)-r*cos(t))^2+(ii(k)-r*sin(t))^2)/s), k = 1 .. n) end proc;

rho0 := 0; theta0 := 0; sigmae20 := (sum(rr(k)^2+ii(k)^2, k = 1 .. n))/(2*n);

l1 := Likelihood(rho0, theta0, sigmae20);

simplify(l1);

Mathematically it should simplify to exp(-n). However, maple seems not able to arrive at this simply solution. What am I doing wrong here?
 

 

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